I got bored, and decided to come up with an idea on how Marvel and Fox can complete the MCU.
Have Wolverine 3 end the X-MEN film universe(I mean I hear it's Old Man Logan) mentioning that there are other timeline's out there, and have the one mentioned be a timeline that features Wolverine alive( since I hear they are going to use Old Man Logan as a basis), so since the Earth is dying have Wolverine and Xavier somehow take a peak into a different timeline which is the Marvel Cinematic Universe, with Xavier saying we never had a group of people like this(referring to the Avengers), saying maybe they can help the X-MEN of their universe to prevent the dying of their world, something the X-MEN alone could not do, have it be the end of Wolverine 3, and a after credit scene showing Tony Stark(Obviously played by RDJ) showing up at the X-Mansion to ask Charles Xavier(I think played by James McAvoy would be a good choice since Xavier doesn't look super old in the Ultimate or 616 comics)
This will be a soft reboot of the X-MEN, making the Deadpool Movie canon to the Marvel Cinematic Universe, Legion is canon to the MCU, Hellfire is canon to the MCU, and Gambit(maybe) is canon to the MCU, but everything else isn't, so First Class to Wolverine 3 isn't.
The X-MEN already exist in the Marvel Cinematic Universe, but like Spider-Man they are unknowns, Xavier doesn't believe mutants should be known to the general public, but the US goverment is in the early day of finding out who mutants are, but at the moment they are just lumped into the same category as Inhumans, and mutates Enhanced , and Powered People.
Have Hellfire deal with why mutants aren't known to the general public, the general public know who enhanced people are, but not particularly mutants, or Inhumans, they all are just seen as enhanced until Magneto reveals who mutants are and his plans for world domination which people end up using the term mutant as a racial slur, an insult to the X-MEN.
The X-MEN could have been formed in 2014-15, and people know about them, but it's kinda like Daredevil, and Spider-Man they are sorta known but not on the Avengers radar yet, Deadpool happens in 2016, and the story behind him is that Weapon X could be working to find ways to unlock dormant X-Genes within individuals like Pietro and Wanda, Deadpool just so happens to be the third HYDRA might know what mutants are, but don't know who is a mutant, and they are the first successes in unlocking the X-Genes within individuals who have dormant X-Genes, Weapon X could be apart of Hydra that works to unlock the mutant gene, with Hydra doing it through the scepter, as a test for Weapon X to see if it works, afterwards they would have sent the scepter to Weapon X, but because of the Avengers, Weapon X had to find another method of awakening the X-Gene that lies dormant in some individuals, Wade is the third success at this.
Legion is happening
Magneto is around but is acting through his Agent Mystique, but he so far has not been a direct threat, as he is preparing his Brotherhood of Mutants and his trying to sway the X-MEN to his side, so that they take the earth for the mutants together, as well as creating a battlestation Asteriod M.
When Magneto because a big threat the Avengers can show up to help the X-MEN stop him and everything, New Mutants takes place after that battle where Emma makes the Academy of tommorow creating the next generation of X-MEN after a disagreement with how Xavier is handling the X-MEN and their way of creating mutant/human peace.
Deadpool 2 happens, Cable comes from the future to setup the X-Force.
Reed Richards is a professor, Johnny Storm(friend of Peter Parker), Sue is Older Sister, and Ben Grimm, Reeds friend go into space(2016) and get lost gaining powers from cosmic rays accident, they travel in space a bit Reed makes their suits from Alien technology, bam you have the Fantastic Four, and appear in Avengers Infinity War.