Xemnas = Ansem
Xigbar = Braig
Xaldin = Dilan
Vexen = Neve
Lexaeus = Esaule
Zexion = Ozine
Saix = Ais
Axel = Lea
Demyx = Myde
Luxord = Lodru
Marluxia = Lairuma
Larxene = Renela
Roxas = Sora
Xion = No I
That's what I think their real names were. Just a random guess, except Axel, Roxas and Xion's ones, since they've already been revealed.
Actually The six original organization XIII members real names are
Xemnas=Ansem
Xigbar=Braig
Xaldin=Dilan
Vexen=Even
Lexaeus=Aeleus
Zexion=Ienzo
besides that, you were pretty much correct one everything else except Saix and Organization members 9-12 since we don't know what their names are, yet.