Timeline!
Comment with the years your people arrived and I will add them in - feel free to mention those who brought them to the school or recruited them or were important in their arrivals.
1888
Wolverine was born "James Howlett", later takes biological father's surname (Logan).
1932
Magneto was born "Max Eisenhardt" in Poland.
1940
Professor X was born in England.
1942
Mystique was born in Germany, parents relocate to New York.
1944
Magneto's parents were taken and murdered by Nazis. He was encamped.
1949
Forge was born in North Dakota.
1951
Charles and Raven met in New York, became adoptive siblings.
1960s (late)
Charles finished university, became 'Professor Xavier'.
Charles and Raven met Erik and Hank, the events of X-Men First Class occurred.
1990s (early)
The events of Age of Apocalypse occurred.
1995
Sentry arrived at Xavier's (via Beast).
1990s (late)
Wolverine and Rogue come to Xavier's Institute.
1997
Zap arrived at Xavier's (via Wolverine in February), meets Forge (her father).