It seems to me, as soon as he gets married, they all will be coming to live with you. A lot of times the new wife doesn’t want to be bothered with his kids. Them calling her mommy is just a title, nothing to get worked up about. Also, didn’t you once post that they call you Eema, so it’s not even confusing to them.
Be prepared to show all the ones who come to live with you an extreme amount of love, but this doesn’t preclude setting down some ground rules!