>>57998774
In the anime canon there's at least two one male one female. It's possible there's a third one, I don't know if it was ever confirmed if the Mewtwo Ash and Goh met was the same as the one from the first movie or not.
It's not too crazy. It makes sense that other people might have attempted to recreate the Mewtwo experiment convinced they'll somehow succeed where Team Rocket failed.
As for the games it's unlikely that the Mewtwo in Kalos is the same as the one in Kanto.