Venting and need advice..

Hello everyone I hope your weekend is going great! I’m in need of some advice. I am currently 31 weeks pregnant and have had a rough pregnancy thus far. I have a 9 year old son and 1 year old daughter from a previous relationship. My boyfriend has no children and his mother who I love dearly is currently staying with us until her home is done being built (Late August/early September). So far this pregnancy I’ve had very bad morning sickness, bad acid reflux to the point where I vomit all day everyday, and now I have been diagnosed severely anemic. With that being said my boyfriends mother babysits his 1.5 year old niece and 9 year old nephew on weekends, his mother tends to throw the kids on me and locks herself in her room so she doesn’t have to be bothered by them. I don’t have any extra energy to deal with those kids and the little girl is BAD and I mean bad as hell. She constantly yells, pushes, hits and slaps my baby girl every time she sees her and doesn’t get reprimanded for any of it, instead the family thinks it’s cute and funny and I cannot stand it at all. It’s to the point that when they come over I grab my kids and lock ourselves in the room most of the day just so we don’t have to deal with them. Well today my boyfriends mother made a remark saying I am acting funny because I keep my kids in the room all day when they come to visit and I don’t let my daughter play with them. I don’t know what to say to her. I feel bad in a sense but also don’t have the energy to deal with that little girl and my baby girl as well. I also don’t like how they do not reprimand her. What should I say to his mother? T.I.A.