Xemnas: ゼムナス (Ze-Mu-Na-Su) so in english, it would be Zem-Nas
Xigbar: シグバール (Shi-Gu-Ba-a-Ru) in english, Sig-Bar
Xaldin: ザルディン (Za-Ru-D-i-n) in english, Zal-Din
Vexen: ヴィクセン (V-i-ku-se-n) in english, Vik-Sen (the i is said somewhat like an e, so veek-sen, but it doesn't matter)
Lexaeus: レクセウス (Le-Ku-Se-U-Su) in english, Lek-Say-Us
Zexion: ゼクシオン (Ze-Ku-Shi-O-N) in english, Zek-See-On
Saix: サイクス (Sa-I-Ku-Su) in