Keep in mind that if you own the rights to a character (e.g. Wolverine), you can still allow Fox to use the character. Just pointing this out in case destroying the X-Men Cinematic Universe is a concern of yours.

Edit: It's difficult to define what exactly you're getting with character rights. Would Spider-Man cover both Peter Parker and Miles Morales? Would choosing Wolverine allow you to use the word "mutant"? Does the Fantastic Four count as one or four characters? Personally, I counted them as four characters when I asked myself this question, but I understand why some people might consider them a single entity. I'll just leave it open to interpretation. Let's assume that the multi-billionaire is rich enough and passionate about Marvel enough to pull some strings and make whatever it is you want possible.

Also let's hear why you're choosing these characters! Any story arcs or team-ups in mind?