One thing that worked for me was to say to my W, in a calm voice that 'if she moved my children away from me, I'd never forgive her'. She didn't move, despite what my SIL wanted to do. You've got to have your b@lls in your hand before you contemplate saying things though, and you have to sound like you mean it, but not in a nasty way. Just another tuppence in the pie!
