Kitty was pretty much out of the Uncanny/Adjectiveless X-picture (with Jubilee taking over the role of X-Ingenue) until De-Aged Illyana was on deaths...
I'm unaware of the "fallen in love with Jean and married Maddie" thing, which may have come much later in the narrative, but in the beginning "dying"...
Nate Grey is from Age of Apocalypse and is one of the characters that crossed over from that timeline. I don't think anyone crossed over from MUTANT...