To take on Mimic Professor X goes out in search of new X-Men. He first approaches the Maximoffs who are still in Europe, but they let him firmly know that they are Avengers through and through and will go down as Avengers as well, so they can't join the X-Men. Wouldn't be surprised if this issue is one of the reasons Marvel can use the twins.
2014 - Captain America: The Winter Soldier | The Amazing Spider-Man 2 | X-Men: Days of Future Past | Guardians of the Galaxy
2015 - The Avengers: Age of Ultron | The Fantastic Four | Ant-Man
2016 - Batman vs. Superman | X-Men: Apocalypse | The Amazing Spider-Man 3
TV - Arrow | The Flash | Gotham | Constantine | The Avenger | Hourman | iZOMBIE
TV - Agents of S.H.I.E.L.D. | Agent Carter | Daredevil | Luke Cage | Iron Fist | Jessica Jones | The Defenders