I doubt that Stan Lee created X-Men. Rather Jack Kirby likely created X-Men.
Bob
Public Enemy #1
Trying to figure out what Stan did and what Jack did is like trying to pry Lennon apart from McCartney.
Leaving aside the fact that the X-Men is a Kirby kid gang and a Fantastic Four wannabe, the central most original character is Prof X. I highly doubt Jack created a man in a wheel chair (or even stole a man in a wheel chair). It's just too un-Kirby a concept. Now a man in a Flying Wheelchair I would believe was Kirby's. (After all he's created two of them). Magneto and the Brotherhood of Evil Mutants. Those I'll believe are Kirby's.