IGN has the scoop from Whedon himself, Scarlet Witch and Quicksilver will be in Avengers 2.
“You know, they had a rough beginning. They’re interesting to me because they sort of represent the part of the world that wouldn’t necessarily agree with The Avengers. So they’re not there to make things easier. I’m not putting any characters in the movie that will make things easier.”
To me this reads that, as I earlier suggested, and what is canon, these two will start out as villains. He talks about their rough beginning (which can allude to their being orphaned and growing up gypsies or to the fact they started out as villains in the Brotherhood), and that they represent people who wouldn’t necessarily agree with The Avengers and won’t make it easier for them (which means they could be villains in the sense that at first they don’t work with the Avengers, but against them, just perhaps not for truly villainess reasons).
Upon some consideration about the twin’s back stories, seeing as they can’t be mutants due to the licensing issues, Whedon could completely ignore most of their background, as they do Black Widow and Hawkeye in Avengers. These twins are simply two people who have amazing abilities with a general blanket statement “this is magic/tech/whatever” and be done with it. They don’t have to go into their parentage or even being raised by gypsies or anything, or, again, just a quick statement to the fact such like BW’s “I’m Russian, or I was” moment. In a movie that will be full of heroes and villains, they don’t have a lot of time and they can probably get away with only some minor background, especially if the twins might be utilized in the Dr Strange movie (my conjecture).
Though, in reality, due to the licensing, I doubt we’ll ever get an origin story for them or their own movie, which kinda sucks but at least they aren’t being completely ignored.
Anyway, at the moment, things are looking good… but please can news outlets stop using the Ultimate’s version of the twins for their stories? This isn’t Game of Thrones people…
X-Men: The (fan fic) Series 
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