Before KH3 and it’s trailers came out my headcanons for some of the characters were:
Demyx wouldn’t of been working for either side but would be the one to reluctantly show Sora how to use water magic.
Marluxia and Larxene wouldn’t of been working with Xehanort instead they would of been minor antagonists who Sora would have to fight at some point because the two of them would of been working together to accomplish some kind of objective that would end up causing trouble for Sora.
Demyx wouldn’t of been working for either side but would be the one to reluctantly show Sora how to use water magic.
Marluxia and Larxene wouldn’t of been working with Xehanort instead they would of been minor antagonists who Sora would have to fight at some point because the two of them would of been working together to accomplish some kind of objective that would end up causing trouble for Sora.