Re: So Ms. Marvel and Falcon are definitely in? Oh and what about Ant Man?
It's not clear who besides the original 6 are in. Falcon certainly seems like a strong possibility since they are including him in the new Avengers Assemble show. However I think we can safely assume that The Guardians of the Galaxy will be appearing. It also seems clear that Ant-Man will not be appearing (in any active way) based upon the news that his film will come out after Avengers 2.
So my guess is: Iron Man, Thor, Captain America, Hulk, Hawkeye, Black Widow, Star-Lord, Drax the Destroyer, Gamora, Groot, and Rocket Raccoon. This is very unwieldy but it could set up a great double team battle against Thanos. It would certainly up the epicness of the fight.
That's a ton of characters so it's unlikely they'll be adding too much more than that. I suppose Falcon and Ms. Marvel have a chance but beyond that I'd be shocked.