I thought your AH was a real obnoxious prat, but wow his mum is the absolute pits.
What sort of malign evil b**ch could treat her small grand-daughter this way? I felt like choking the #&>>#@$%% at the very least.
Tell her next time she calls, that she is a nasty and miserable piece of work and you don't want her anywhere near yourself or your precious children. As for daddy....let him know that if he can't see what poison his mum dumps on his kids is bad for them, then he is even sicker than you thought he was.
If it is impossible to tell these creeps this, then keep it in mind and limit contact to as little as possible.
You have done wonders with this rotten situation and I do admire you so much.