(Note: I tried commenting on your comments but it didnt let me for most of them)
In the bonus chapter 'The Bromance' they mourn him pretty damn well, because the wound is fresh. In the Epilogue, they have gotten two years to recover and are slowly moving on. Dan didn't cry, because he didn't usually show many emotions. Aspen DID have a long speech bc. she was the one closest to him and mourned him a lot. Jonathan was too young to understand and didn't get that his father was dead. I know some three-year-olds can wrap their mind around that concept, but Jonathan didn't get it.
Jonathan is around twenty in the last bonus chapter and Aspen is in her mid-thirties to early forties. They both agreed on a date where Jonathan would take over, but he would be older than the general Alpha. Jonathan didn't think he was selfless enough, intelligent enough, or powerful enough to fully commit himself to the pack and Aspen knew that too. So, they both agreed that when Aspen was in her sixties, Jonathan would take over.
Jonathan doesn't mourn Maximus because he's had seventeen years to recover. He instead celebrates the life his father lived and the things he accomplished. Besides, Maximus didn't want to be mourned over, he wanted people to be happy.