Well the ideas of the Tyranids rebellions and established their own Hives somewhere across Hell rings, it's all started when many of the Tyranids thinking that if they stay complacent like this in the time of peace the Tyranids would grow weak, soft, and useless, so they decided to rebel and establishing their own Hives.
          
          So they secretly plotting when large groups of them seperated from the Hive-mind for planning rebellion, and undermining the Leadership of the Swarmlord and the main Tyranid Hives that remained loyal to Charlie and her allies, but what various Tyranids did not expected is that there is so many with various ambition and agendas.
          
          Tyranid ground leaders include, Trygon Primes, lesser Norn-Queens, and unique, powerful bioforms, like new powerful prototype Bioforms even Bio-titans, and the newly evolving various of Tyranid leaders. Other leaders and command units include the Tyranid Warrior Prime, Genestealers Broodlord, Tervigon, and Maleceptor, all of whom lead lesser troops and direct the swarm through the central Hive Mind. 
          
          But in this case many of them are going rogue to establish their own domains by claiming territories they conquered across the rings of Hell, that they now own by the right of congquest and operate the territories as their own kingdoms.
          
          That including various of dangerous crossbreeding hybridization experiments which they conducted to create new powerful prototype Bioforms, and evolving the current bioforms into better new powerful forms, with the strength to matching the Swarmlord one on one combat and other powerful Bioforms.
          
          Well the inspiration for the Tyranids rebellions was inspired from this comic below, where a boy name Slade got shrunk down into the size of a tiny human called Myte by a magical amulet, and meeting various race's of tiny people that live besides insects and arachnids even riding and using them as steed and beast of burden, let me tell you it's awesome.
          https://youtu.be/82O-Nuocql0?si=SeLOBzZBTc2Pnr9Z

Some fixing, for the Morningstar Imperium on the last part is, despite facing many opposition from many enemies they never giving up.

The wasteland stalkers: A group of Tyranids who live in the Ring of Pride wasteland in the outskirts of Pentagram city. Whilst largely nomadic, they also have a single city called "Swarm City", built inside a great underground cavern with tunnels.
          
          Morningstar Imperium: Proud, Imperium of Man-eque Tyranids who live inside of the labyrinth and consider themselves as the most largest powerful group and loyal Tyranids to Charlie in Hell. Despite their Imperials appearance after some copying and took some inspiration from the Imperium of Man, but instead they're demonic in terms of appearance. But they do really intend to changing for the better despite facing opposition from other many enemies they never ging up.
          
          The Wrath raiders: A warlike Tyranid group that lives in the Ring of Wrath and allied with the local Genestealers and huge herds of animalistic Genestealers.
          
          The flies of the Honeyed Thicket: A peaceful Tyranid group allied with Beelzebub and serving as her servants, bodyguards, and mercenaries.
          
          The Locusts of greed: A Tyranid group that allied with imps and shark Genestealers ruling their territory, through strength, money, and with some mafia style in the Greed ring.
          
          The unseen claws of the puppeteers: A group of Tyranids that prefer to stay in the shadows of Sloth ring, prefering for secretly controlling society by infecting them and manipulating them to do their bidding, although they will secretly assassinating anyone who is a threat to them.
          
          The butterflies of love, lust, and ecstasy: A Tyranid group with a lust and ecstasy aesthetic into themselves using their evolution to gain the ability to produce aphrodisiacs pheromones that induce lust and ecstasy, they also allying with Genestealers in Lust ring.
          
          The Sea Devils: A bloodthirsty Tyranid group that lives in the ocean of the ring of Envy, and allied to the ocean Genestealers creatures, they rule the waters with an iron fist and preying on anyone that dares to get close enough to their territory.

Wait no, not eighteen, but instead thirty two Tyranid groups which rebelling from the main Hive, and wrestling for the control of Hell, with other groups as well are fighting and killing one another, in the aftermath with most of them are wipe out and eradicated during the war, except the eight main group that still remain around after the war.

Also ImaginationAve I got this new idea about the rising of internal conflicts within the Tyranids Hive, due to many disagreements and complaints of unnable of hunting down and eating anymore of the local natives to consume their biomass, which in the future gave birth to a dozen factions within the Tyranids. 
          
          It will be interesting in the future of your story that a large number of Tyranids are not approving with the changing of the status quo for peace, because they believed the Tyranids would grow weak in time of peace and sought to undermine the peace by just simply left and established their own hive in their own conquered territories. 
          
          After sometimes a very vicious civil war erupted between the original Hive and at least eighteen fledgling groups for dominance. Over the course of the war, the number of rival groups shrunk down to the original Hive and seven others that each group now own and operate on the rings across the realms of Hell they have as their own kingdom.
          
          Once the small timers were gone, the eight main Tyranid Hives have wrestled for control of Hell. Lots of blood was shed both from combatant and civilian even the Imperials are not spared from the crossfire of their Civil war, and in the end a truce of peace are made between the eight Hives after the war ended.
          
          Even though each Tyranid groups are now owning a territory on each ring of Hell which they conquered, even many of the Hellborn Demons and Sinners, including the seven Sins, the nobles of Hell Ars Goetia, and other noble families as well, are scared shitless, and don't want to mess with them at all, especially since the Tyranids civil war causing so much damage to literally everything and everyone around them.
          
          Although for the pro-war Tyranid factions themselves, their war and conflicts are simply known as the great winnowing, a process where the weak are removed and purged with extreme prejudice, so that the strong may thrive without any weaknesses holding them back.

I've meant on that last part is, now in his weakened state now Angron is absorb and assimilated.

Also I got this idea where in the aftermath of the war against the invasion of Khorne and his Legions, some of the Tyranids during their patrolls and scavenging on the remains of the battlefield, accidently found Angron who is already greatly weakened by the war.
          
          Seeing Angron weakened state the Swarmlord decided to absorb Angron and assimilate him to gain his powers and abilities. Just like how Kaiju no 9, from the series of Kaiju no 8. Seeing that Kaiju no 9 have the ability to assimilate other living being into himself and gained their powers and abilities, and he use it to absorb Isao Shinomiya to transformed himself to become even more powerful. The Swarmlord also do the same thing to Angron by absorbing Angron into his own being, remembering that he defeated the Daemon Primarch with the Help of Charlie, his forces and Imperials, and flung him far away from the battlefield. And now in his weakened state no Angron is assimilated.
          https://youtu.be/ZPuevK0Phbk?si=H9kVNXlf0yViIOa3
          
          Especially after a very, very, VERY long time in the mental world, but not too long in the real world since the realme of the mind can moves fastsr, where the Tyranids imprisoning Angron consciousness for questioning and Charlie also helping on calming Angron down. In the end after calming him down after years of imprisoment in the Hive-mind Angron decided to tell his tales to them on how he become a monster in the first place
          https://youtu.be/YPQO7Lv1660?si=y3ZX04dPgXn-47bf

Also by the way, putting aside from the Exorcists origin and stuff like that, imagine in the aftermath of the war against Khorne Legions and after the Swarmlord being reborn after the massive Khorne explosion.
          
          He tell Charlie that after his rebirth after sometimes, he have this dark thoughts and desires to unleashed his growing rage, and there have been several mood swings that came without any warning.
          
          "It feel's like I'm changing into something else entirely".
          
          "These dark feelings are bubbling up from my chest".
          
          "I want to go wild and destroy everything".
          
          "I just want to raise my hands against everyone...".
          
          "I've never felt such irritation...and anger before".
          
          "Charlie please listen, for some reason I can hear and see Khorne, and feel all of the anger and rage from all of the living beings in the Universe in my mind and dreams, and without connecting to the Hive-mind it feels like I could suddenly without warning I will losing control of myself and going berserk without any control".

Hey ImaginationAve I've been wondering about something for a while, specificly about the Exorcists origin or what are they, and found something about their origin in Heaven's army and roles as well.
          
          So I've guess after this revelation below, you may going do some rewriting on your story, sorry about that.
          
          Exorcists in Hazbin Hotel Universe are heavenborn angels, not human souls. They are created and raised in Heaven to serve as a heavenly army, and they are distinct from human souls who go to Heaven (called "winners"). 
          
          Heavenborn: Exorcists are beings native to Heaven and were created as angels with specific roles to perform.
          
          Not "winners": They are not human souls that ascended to Heaven. A key point is that while some Exorcists like Vaggie may have human-like traits or speak a human language, this is part of their individual design and doesn't mean they are human souls.

Imagine when the Tyranids and their Genestealers are going to take Heaven, and they are going to take it!!... However instead of coming and overwhelming them with guns and bombs like the forces of Heaven and their leaders suspected, mistaken them as pack of disorganised beasts and mindless animals, they instead hit keypoints, confuse them, and simply take over the infrastructure!!.. We've already seen what would happen if several mobile phone carriers received an attack. So the Tyranids Genestealers are this.
          
          1. Interrupt the internet, telephones, TV, radios, and blindfold the general public...!!
          
          2. Attack the administration, politicians, and cease the functions of Heaven.
          
          3. Then finally, gain control of the Heaven eletric power company and Exorcists force bases...!!
          
          After that it would be more than billions of citizens of Heaven panicking in the darkness vs about roughly more than 200.000 Tyranids, alongside their most powerful super-hybrid regiment and their Legions of Genestealers that have been using the citizens of Heaven as seedbeds and breeding hosts for their offspring including DNA donors to increase their numbers during their time of infiltrating Heaven Society.
          
          And then the kingdom of Heaven would be controlled by the Tyranids and their Genestealers in a matter of few days, well considering how big Heaven is compared to Earths and Hell it's going to take a while, but since the Tyranids already have the Genestealers weakening the defenses of Heaven it's going to take a while.