It appears that we've got more movement on the Avatar sequels. While the next movie isn't due until 2020 they have begun the task of casting new faces to go along with returning cast members of Sam Worthington, Zoe Saldana, and Sigourney Weaver. They have their first name in Cliff Curtis from Fear the Walking Dead according to Deadline. Curtis will play "Tonowari, who is the leader of the Metkayina, the reef people clan." Production for Avatar 2 is set to begin next year and the movies will work around Fear the Walking Dead.
The deal he signed also brings him on for all four movies so there goes any tension as to whether or not his character is going to survive.
Avatar 2 may or may not be released on Dec. 18, 2020 with the following sequels coming out in 2021, 2024, and 2025.