Ash's sun and moon

Ash and pikachu have traveled a lot of places and met a lot of pokemon, one day after ash's last travel which was unova, ash has a strange dream of seeing two amazing pokemon

They entrusted ash with their offsprings, now ash has taken care of the 2 pokemon with his mother ever since, how will it change when ash and his mom head to alola?

What will happen to the off springs?
More importantly who were those 2 pokemon from his dream?
And who are these off springs?
And what secrets lie in alola?

That's for us to find out as the journey continues