Is it me or does X-Men First Class doesn't exactly fit to the story of the Originals?

i mean in X-men The Last Stand, A scene where Charles and Eric both at an old age, visit Young Jean. But it turns out in the New Film that they become archenemies when they are only young, and also Charles ends up in a wheelchair at a young age and in the originals he is walking in the flash backs at old age. Whats up with that? Also where did all the other mutants from the newer virsion go?