Plot Hole Mania
Cecil becomes a Paladin...and then murders his brother? Yeah, that's what a Paladin would do. Good call.
Celes killing the LAST BOSS of Final Fantasy 1 by herself?
Yeah, ok.
You realize Cara is a little girl where as Cyan is the Royal Knight of Doma? Wearing full plate male. A chakram (not flying disk..) that hits him would not even knock him slightly.
Oh, and Sephiroth is a little girl, he couldn't do anything nearly this cool. Since you are combining the various Final Fantasies, regardless of what the fanboys say (read: you) Kefka would own the junk out of Sephiroth and take the show away from him.
Also, the previous poster is yet another FF7 fanboy. Cloud would get TOTALLY destroyed by Zidane. A whiny baby against a thief? Zidane has finesse, where as Cloud would try to use brute force. Winner = Zidane.