Since Origins Is cannon we can't have Cyclops and Jean In film as teenagers In 1973.If Origins was being Ignored then they could fudge It a bit If you say the trilogy took place around 1994.
Banshee and Havok will likely be recast.
As for brotherhood Angel and riptide could be dropped and emma could also be recast.
The actor who played azarel will likely be back.Rose Byrne could also return If Moira Is in film.Xavier could also already be bald when film opens.
As for event which leads to sentinles possibly Brotherhood attacks washington over the weapon x and other experments on Mutants(Tie In to Origins)
If they want to stick to original comic of mind transfer they could have It be Xavier switching minds and he and Beast,Havok,and Banshee VS Magneto,Mystique,Azarel,and emma.
With 10 years later If Moira Is In film she could have become a scientist In that time.
Perhapes working on something and reporting to Xavier on project.