>>90512550X-Men and X2 are hard canon. They happened no matter what.
In the old timeline, they were followed/joined by X3, Origins, and The Wolverine. First Class was also canon to this timeline.
Then DoFP happened and retconned X3, creating a ripple that altered details of the other movies. For instance, Wade Wilson ends up becoming Deadpool instead of Weapon XI. We can assume that some events played out similarly (Logan goes to Japan, gets dogtags from Weapon X, etc.), but the big game-changer events (Scott, Jean, and Xavier dying, Gambit not being Channing Tatum, etc.) all got un-done so that the franchise could continue cleanly.
The Bad End future from DoFP was present day (unless I'm mistaken), but that shit was fixed by sending Wolverine back to the 70's.
>tl;dr>Days of Future Past retconned any major character deaths/contradictions in continuity, while everything else can be assumed to have played out in more or less the same way