How to handle SIL who is obsessed with hubby ex and antivax

Ok, I understand people have their beliefs. I’m not looking to be attacked or bashed. Nor do I want my SIL to be. Let’s be civil. Sorry it’s long.

I am a 31 year old mom of 2 sons (a 6.5 year old and 2 month old). My first son is not my husband’s (35 year old) but he has been around since 2018, we got married 7/2020. I have never met my SIL because honestly she wants my husband back with his ex wife and at first we lived states away. I did live one year in the same state and she still didn’t try, instead still telling my husband he should fight for his ex. Our son is born and my husband’s mini me but before that she asked him if he would get a paternity test! She doesn’t know me and I have never cheated. Baby conceived on our wedding anniversary.

Without discussing with me SIL and MIL decided and booked a vacation. SIL has 8 children (20 years old to under 1 year old). She does not vaccinate. I do but my son only has his first round of vaccinations. She does homeschool but she also brings her children out and several times now gotten them very very sick. On purpose, almost ending in several being hospitalized. My first son is immune compromised, a normal cold to him turns into pneumonia and a month of nebulizer treatments. And my second is a baby. My husband does not want them around but has not said anything instead choosing to ignore them. I am in a weird spot now as they have sent texts counting down 😕, I guess they arrive in a week.

Additionally, I’m frustrated with my husband. This is his family, and his lack of communication has become a huge issue. Our lease ended June 1st (they rented a house in the town we lived in for this vacation) and we were supposed to be moving back to his home state and staying with his dad while we get a house. He has not confirmed a thing! We are now all in my mother’s mobile home last minute (45 mins away from where they are staying when they thought they’d be minutes). I told SIL we do not have our apartment anymore and received no response. I try to make plans and do things to which SO ignores. How do I handle both the situation with my SIL and my husband? I think he believes we can just ignore them when they’re here and to me that’s horrible.

Help.