Jake Sully and Neytiri are locked in.
We already knew that James Cameron had some big plans for the Avatar franchise by making not just one but three sequels, and now he's officially signed the stars from the first film to reprise their roles. According to The Hollywood Reporter, both Sam Worthington and Zoe Saldana have signed on for the new trilogy. In case it's been a while since you've seen the 2009 original, Worthington played Jake Sully, the human who ends up having his consciousness permanently transferred into the body of his Na'vi avatar, while Saldana (Star Trek) plays his love interest Neytiri.
The other cast member that will be appearing in the new films is Stephen Lang, who played the brutish military commander that dies in the original film. Whether his character will be appearing thanks to some mind-body transfer trickery, in flashbacks, or another capacity altogether isn't yet clear — but the Reporter does specify that Worthington and Saldana's characters will have children of their own in the new films. The first Avatarsequel is schedule to be released in December of 2016, with the subsequent films appearing at yearly intervals.link