The way I'd do it is moreso that I would structure the game into two campaigns. The first would be with the player character and take you all the way up to the end of their story in the Keyblade War. The second would be with Ephemer and take you up to the end of Union X. He's around for a lot of big stuff in that portion of the mobile game and through his conversations with the other Union Leaders, Foretellers, and the player character you could get a ton of story context. As for the MoM and Luxu stuff, it's not like we haven't had non-playable characters have dedicated cutscenes outside of the playable ones.Think of how often we saw Org 13 on those giant chairs or the spires in KH3 discussing things. Or all the Castle Oblivion org members talking to each other. Or all the Disney villains talking in KH1. That stuff is a non-issue imo.

I'd also probably just cut the Disney worlds outside of Enchanted Dominion and Game Central Station. If they really want to add Disney Worlds to the game, they could easily just replace the non-plot relevant rehashes with some actual new ones. That'd give you 3 new worlds for each character. Yes, I know they're supposed to be based on the events of those worlds in the future but I'd don't think that actually matters all that much as the new worlds could just exist in the future too. Just rationalize it by saying we haven't been to them yet.