Need advice asap

Long story short. My mother in law can be a lot and my fiance can be blinded my her . So we made an agreement about family and covid. And only his dad has been tested and hasn't gone out but nobody else is allowed in the house because of our son. We made an agreement. A week after, he says I think I'm going to have my mom come over. I asked him if she has been tested, symptoms, etc. He told me that it's fine and that she doesn't want to get tested even if she feels under the weather because she works at home now but doesn't want to get tested because it will jeopardize her job. I told him about employment laws that she can take time off and not use her sick hours and get paid. How the information is confidential anyways if she gets tested. He told me it isn't black and white. I had to step aside for an hour and I came back and already told her it was ok. So putting my foot down didnt work. She's coming rn and Idk what to do. Should I be kind and just make sure she doesn't get too close to my son or should I stay there for a bit and pretend that I have errands to run and take my son ? Please give me advice asap