Alright, so, i can think of two ways that this can go, i would really appreciate some input on which you guys would prefer.

1) What Double suggested. We are a team, working together to fight our way through worlds that are getting taken over by the Heartless, stopping them and the plethora of Disney and Final Fantasy villains that are controlling them.

2) We do more of a shared open world sandbox. Essentially, everyone is here to tell their own story and they don't need to worry too much about what everyone else is doing. You have your own story arcs, explore your own worlds, have your own supporting cast, your own main nemeses. Every so often, something big happens and all of the characters are brought together for a big boss fight, but appart from that, everyone is free to do as they please.