No surprises here, but in case you were wondering, Sam Worthington and Zoe Saldana have officially signed on to star in the three Avatar sequels being developed by James Cameron. I just assumed they were were already on board, but apparently not. The only other actor that is officially attached at the moment is Stephen Lang, which was much more of a surprise than this latest update. He played Marine Colonel Quaritch in the first movie, and he died.
Cameron plans to shoot the films back to back to back. He hired several screenwriters to help him through the process of getting these films made. Those writers include Josh Friedman (War of the Worlds), Rick Jaffa & Amanda Silver (Rise of the Planets of the Apes), and Shane Salerno (Savages). Avatar 2 is expected to be released in December of 2016, and each year after that we should get a new one.
There's no official plot details at this time, but apparently Jake Sully and Neytiri will have kids. Cameron had this to say about the return of the actors in a statement,
"Jake Sully is a rare combination of passion, strength, street smarts and soul, which requires a lot from an actor. Sam brought to the role a combination of sensitivity, vulnerability and strength. Zoe captured every aspect of the character I envisioned, bringing to Neytiri a mix of delicacy, fierceness and incredible physicality. I am beyond pleased they'll be returning with us to Pandora."