Mother in law with Mental illness is hard!

No offense to anyone else, truly. How do you handle needy mother in laws when you share children? We aren’t married but he can hardly go anywhere without her calling multiple times or getting asked for something. He was in his car to go to work here she comes asking for a ride to the store to get toilet paper, knocking on his door and banging on the door knowing he has to go. He kept telling her no and me and our son got off the phone with him. We went somewhere yesterday and she called alot and he answered because she does have a mental illness so he worries but she mainly needs help in some way or something small. It feels like another child, sad to say. It feels toxic and this is why my son and I don’t visit. She is aggressive and goes off the handle at any moment. I have had alot of patience and I consider the circumstance, but it also puts me in a hard place to handle our child 24.7 because it’s not safe for him to do so.