I feel as though that the Seven Guardians of Light are fairly easy to figure out.
I've intentionally selected Roxas as opposed to Ventus because I feel that Sora would find the Key to Return Hearts and make Roxas a complete being. Plus, Ventus is being heavily hinted to be a possessed Seeker of Darkness with his affiliation with Vanitas and the 0.2 Birth by Sleep opening.
Um, Sora IS Roxas's complete being, as is Ventus (he is both their nobodies) ergo Roxas being able to be made into his own being is absurd.
Furthermore, how is it "heavily hinted" that Ventus is a seeker of darkness?
Vanitas was spawned as a separate being and Ventus landed himself in the awakening chamber because he resisted the darkness, the latter was pretty much the ultimate resistance.
I'd be baffled if Ventus weren't a guardian, Kairi quite the opposite.
If the Princesses of Heart are a part of the light that the guardians protect than Kairi can't sensibly be both can she?