[@King Kindred] generally, the way I used Star Wars characters was that the characters are mostly just "Those who also travel the space between" No grand explanation, they were just there, because they fit a narrative need. Again, like the Final Fantasy characters. One of the ones I did was a bunch of the Bounty Hunters like Bossk, IG-88 and Greedo as well as Rocket and Groot showing up to Snow White world when Grimhilde put the hit out on Snow White.

Jedi were "Another order of Heartless Slayers that Maleficent killed off decades ago by tricking one of their order into killing the rest" Vader was an implied force rather than ever actively appearing. (Primarily because one of the characters in the campaign was essentially playing the Roxas to Anakins Sora.)

Also, yes, I agree with the Princess Hearts needing to be pure, but that doesn't mean they can't grow dull. There was a whole plot point where one of the Nobodies managed to capture Queen Brahne's heart after she was killed (It was corrupted, but still monstrously powerful and afterwards the gang had to let it go because it wasn't any good for the Kingdom Hearts project)

One of the other ones I did for Atlantis was that The Heart of Atlantis is essentially an imperfect Kingdom Hearts. A load of Princess Hearts cobbled together, but with a few darker ones also spoiling the mix. Again, more powerful than you could possibly imagine, but nothing compared to the real one. There was also a whole thing about Star Butterflys Heart being an "Almost Princess Heart" like, she was so close, but it could still go either way. They have to be earned, not born with.

Pretty much, "Not every Princess has a Princess Heart, but all Princess Hearts belong to someone who is a princess in some way" like, one of the princess' was Marie from Aristocats. Mostly because O'Malley and her brothers kept jokingly calling her "Princess"