Originally Posted by Hawkingbird
Well, the fact that in X2 we see the names "Maximoff" on screen may answer the rights question
Several months ago, Kevin Feige was asked specifically about Scarlet Witch and Quicksilver. He said that the film rights are complicated/open enough that BOTH Marvel Studios AND Fox can use the characters; it's just that Fox's Wanda & Pietro can't be part of the Avengers, of course, and MS's Maximoffs can't be children of Magneto. In other words, Fox gets X-Men/Brotherhood Maximoffs, and MS gets Avengers Maximoffs.