You shouldn't forbid your in-laws from seeing your kids.
Fred is at home when he gets a call from his father in law Bob asking to visit to see his grandchildren.
Fred wants to respond to Bob's request for a visit.
Fred tells Bob that he doesn't need to ask to see his own grandkids and that he can come over anytime.
Fred tells Bob that he doesn't really want him coming over as they have plans, and he'll talk with him another time.
Bob is delighted and gets excited at the prospect of playing with his grandchildren.
Bob is hurt that he can't see his grandchildren and feels out of the family loop making him even sadder.