The darknesses.

[bladewarrior13]

What about Xigbar and Saix? They have been revived as Braig and Isa, but Master Xehanort is around and Xemnas is too. It sounds stupid because they will basically be the same character, but its a possibility and they need some people to fill the empty spaces. After the confirmed ones, the only ones that have been speculated as being very likely are Vanitas (almost definite) and Terranort (highly speculated) so they need some others to fill out the roster. I also could see Dark Riku is possible because he is a past incarnation of Xehanort. That would be 11 so they still need two. IDK???

 

[Sephiroth0812]

What about Xigbar and Saix? They have been revived as Braig and Isa, but Master Xehanort is around and Xemnas is too. It sounds stupid because they will basically be the same character, but its a possibility and they need some people to fill the empty spaces. After the confirmed ones, the only ones that have been speculated as being very likely are Vanitas (almost definite) and Terranort (highly speculated) so they need some others to fill out the roster. I also could see Dark Riku is possible because he is a past incarnation of Xehanort. That would be 11 so they still need two. IDK???

Xigbar/Braig and Saix/Isa cannot be compared to Master Xehanort and Xemnas. The first two have the same consciousness and mind, just like Axel/Lea or Zexion/Ienzo. Master Xehanort and Xemnas however, just as Ansem SoD, too, have different and independent consciousnesses and minds, just like Kairi and Naminé as well as Sora and Roxas. They're all special cases that, while they come from the same source, count as different characters because they are their own "people" to some degree.

Furthermore, it isn't yet clear if these two are really "Braig" and "Isa" at all, since the former is addressed the whole game as "Xigbar" while Lea only exclaims "Isa" on recognizing the appearance, there is no real confirmation which one of them it is.