Mother in law

Okay my sons dad still lives at home with his parents, he’s in the process of finding a place but until then he’s living there. Well his mom acts like she’s my sons mom and won’t let his dad be a parent. Just recently he told our son time to get off the Xbox and get in the bath then bed, mother in law chimes in with “no he can play till I’m done(with whatever she was doing on the phone) and when he started to give him a bath she storms in and is telling him she can do it and shuts the door. I’m just blown away by this and They got into afterwards about it. She just doesn’t know boundaries, she doesn’t understand she is not his parent that his father needs to be the parent and she doesn’t let him... were at our wits end with her doing stuff like this no matter how many times it’s addressed nothing changes. My sons there 2 days during the week and every other weekend and I’d hate to have to keep him from going over there bc he needs to see his dad but I cannot deal with her 😩