They have not yet decided, yet written/filmed, if there will be a season 4. However, Tasie Lawrence (actress of Mara) tweeted that if there is enough demands for a season 4, that they will make one, but Tasie will not be on House of Anubis so this means that más than likely Mara will not be on House of Anubis.
As for if Nina will be in season 4, it's not likely. Natalia Ramos (actress of Nina) dicho that she no longer wants to play the part of Nina (at least this is what I've heard, IDK if that's true). If it is true, then Nina will no longer be on the show. Since Nina was not on season 3, then she may not be in season 4.
The good news is that there WILL be a movie! Alex Soyer (Actor of Alfie) comentó on a tweet that asked if there will be a movie saying, "IDK when it will air". So unless Alex is lying, there will be a movie but the fecha is unknown. The odds of Natalia (Nina) being in the movie is not likely and the movie will be Tasie's last appearance on the show, and más than likely Mara's?
posted hace más de un año
The movie is true. But is unconfirmed about Nina, though. Miss tu Nina!