The film rights to Marvel comic-book characters in the universe of Hollywood is, as Marvel Studios chief Kevin Feige put it in an interview with HeyUGuys, "pretty cut and dry." 20th Century Fox owns The X-Men and the X-men mutant universe, Dardevil and his world and The Fantastic Four and that comic book's millieu. Columbia/Sony owns Spider-Man and Ghost-Rider and for the most part Marvel Studios owns everything else ("The Avengers" and all the characters within are obviously their biggest brand).
However, there are a brother and sister pair of mutants that evidently have tricky rights. According to Feige, both Marvel and 20th Century Fox could use Quicksilver and The Scarlet Witch. "It's a little complicated," he said about the rights issues around these sibling characters. "If they want to use them in the 'X-Men' movies they could, if we want to use them in the 'Avengers' movie we could."
This is likely because Quicksilver and the Scarlet Witch, twin mutant characters and the son and daughter of X-Men villain Magneto, and were at one time members of both The Avengers and the X-Men in the comics. The Witch is a mutant with the ability to manipulate probability via her "hexes," while Quicksilver can run at a lightning-like speed.
Could these characters be used in the inevitable "The Avengers 2"? Feige won't say, likely because that sequel is further down the road. "Iron Man 3," "Captain American 2" and "Thor 2" would all come first but whenever the next 'Avengers' does eventually come to pass he "suspects new characters will be ceded into the mix as well."
Feige is right to not be definitive. An 'Avengers' sequel would probably not arrive until 2015 at the earliest considering all the groundwork and solo-film mapping that needs to be carried out first. Regardless, Feige says the Quicksilver/Scarlet Witch rights situation is "unique" and very few other characters share this distinction. Coincidentally, The Avengers villains The Skrulls are also co-shared (by 20th Century Fox we assume), but the Marvel chief says this isn't the reason they didn't use them as the antagonists in the film. "Joss had a lot of story going on," he said. "The last thing we needed was shape-shifters and getting into that end of the world so it was never the intention of shape-shifters or Skrulls.
And as for one of the early Avengers founding members, Ant-Man, who is still missing in action from the Marvel Universe, Feige does give an update on the Edgar Wright and Joe Cornish-written movie, but it's pretty much the same story we've heard over the last six months. "It's as close as it's ever been and Edgar is excited to get behind the camera again and start some advanced prep work for 'Ant-Man.' We're going to take some forward movement with it... but as far as a release date, I don't know."
As of right now there are two Marvel films slotted for 2014. "Captain America 2," set for April 4, 2014 and an untitled and unannounced slot already carved out for May 16, 2014. Marvel nerds will remember that a June 27, 2014 date was also etched out in advance for an unannounced Marvel film, but currently it's not on the release date calendar. Could "Ant-Man" be one of those films? Feige better hope they figure it out soon as Wright's dance-card is beginning to fill up.