Re: The Avengers 2! The Official News and Speculation Thread - Part 1
OK from the man himself:
"We both have them. There’s a specific arrangement with those two characters that would allow us to use them with Avengers, but not discuss or reference their mutant or Magneto-related lineage. They can use them as mutants and as Magneto’s relatives, but cannot have anything to do with The Avengers." - Kevin Feige
There you have it.
“Whenever you see somebody crossing over to something it gives it pop. Like Murder She Wrote and Magnum [P.I.] — great crossover. I got excited.” Joss Whedon on Spider-man joining the Avengers.