I dunno about you guys,but this is what I think thier real names (Before they were nobodies)are.By the way, in case you didn't know, each member's name has an x in it. Take out the x, unscramble the letters and you have your name! Also some of these names are proven.
Demyx- Demy (I think so)
Roxas-Sora(DUH DUH DUH!!)
Saix- Sai (it's also the name of a type of weapon.)
Marluxia- Milarua OR Amilrau OR Ramuali ( I couldn't pick which one to use).
Xion- She has no real name. You could call her Sora or Noi but neither of those are right.