I´m not sure if this is off-topic, but i heard that before fight with ES in Final Mix he says:
"Aqua... Ven... Keyblade... who are you? I can feel it... we have met before... it was when... No... it isn't you... It isn't you that I have chosen... Why is it not him... Xe... ha... nort... is that you? Xeha... nort... Xehanort!"
If he really says so, could this mean that two of those knights are Ven and Aqua? I think BHC would be Aqua and Roxas look alike would be Ven. Or would brown haired knight be Ven? I don´t think so, ES-knight is too big, he can´t be Roxas look alike. OR maybe ES is new character? Not one of those who were in SE? I can´t think blonde as Ven. He´s just like Roxas. Maybe it is him? Maybe this scene is before he met Organization XIII.
And brown haired knight, he just can´t be Xehanort. Xehanort has brown eyes. But he could be Saîx. He has the same hair style. Even their noses are alike. =D
And Saîx is obsessed with hearts. Maybe because of his past?
BHC, IF her name is Aqua, she could be connected to Kairi. (Think about it. Kairi and Naminè are both something like "sea" or "wave" or "ocean".) Even if BHC isn´t her nobody or anything else like that. Maybe Nomura is just playing with us. He´s evil. :/
Well that was almost all. I just want to say again that I didn´t translate what ES says. I hope that she/he isn´t mad for me now! And I hope you understand what I said. (I don´t speak english as my own language, so there can be huge errors.)
Just my stupid speculations. I hope someone enjoyed. :P
Ps. Maybe Ven is Vexen? If ES is Saîx, it would make sense. Ofcourse they were normal people when SE scene happened. Maybe ES is his heartless, who is searching for Ven? My brain hurts... I just hate that stupid Nomura.