Re: Question about characters
Fox can use them because they're mutants, not necessarily because they've been in X-Men comics (which they haven't a whole lot). Marvel can use them because they're full out Avengers characters. Other characters like Beat and Wolverine don't count because they clearly fall into line with X-Men comics, while Pietro and Wanda don't. It's that simple.
Any and all mutants go to Fox.
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