Now in terms of whether Sylvester Stallone was on board this project, I kept reading conflicting news for a good long while. But it has been confirmed that he is on board and is even helping in the writing process. Don't forget, Sly wrote the first Rocky film which won an OSCAR for Best Picture, Best Director, Best Editing and was nominated in 6 other categories that included Best Original Screenplay. Sylvester will of course reprise his role as Rocky Balboa and play trainer and mentor as the now-retired Rocky Balboa.
Michael B. Jordan has been offered the role of Creed's grandson, I haven't heard anything about Tony Burton (Apollo Creed's trainer) appearing, hopefully he will. The script is being written by Coogler and Aaron Covington.