HELP!! How to deal with mother in law and her dirty house.

I just recently had a baby, my mother in law has been asking to baby sit and have her over all the time but the thing is her house is really dirty to me, the walls in the kitchen are caked with oil, the picture frames and walls are so dusty you can tell they haven't cleaned them in years, apart from the couch and their beds they have stuff stacked on chairs, side tables, and in their bed rooms, they don't even clean their bath tubs or restrooms well either, I end up putting toilet paper on the seat when I use it, that's how grossed out I am. My ex says that the baby needs to build her immune system which I understand but we're talking about people that passed a staph infection like nothing, out of 5 people only 2 people didn't get it. I don't feel comfortable leaving my baby there at all but we just seperated and now are dealing with figuring out what days he's going to have her etc (he lives with his mom and even shares a room with his little brother, whereas I have my own room and bed for her and an extra room adjacent to mine). What do I do? Can I tell him she's going to stay with me? we live 15 miles apart. She's only a month old, she hasn't even had her shots yet. They're all able to clean but they choose not to, Im not a clean freak by any means but I do have place for everything and I try to keep everything clean like any normal person. Amy advice? If we go through court will they allow him to keep her even though he shares a room with his brother? Not sure if this is relevant but we live in CA