I need some advice about my in-laws

So my SO, 2 week old son and I had gone over to their house for Christmas. They usually smoke their cigarettes downstairs but their basement is getting redone so they stood at the front door while they were in the living room to smoke. Smoke doesn't go in just the way you blow it so it was getting inside the room too... Where my 2 week old son was at and breathing with his healthy, infant lungs.

My MIL also kissed my baby on the mouth. I told her that I don't appreciate that sort of thing because he could get sick and that I don't want anyone doing that no matter what. She said she only kissed his nose but I watched her pure as day kiss him on the mouth. Then she went into this big old rant about how she never did that to her kids so she definitely wouldn't do it to her grandchild. And then my FIL rudely pushed pass me and ignored me because I guess he didn't agree to me saying that to his wife.

His parents are the aggressive, "don't tell me" type of people and I've always been kind of passive and a people pleaser. Which I'm trying to work on speaking up and not caring so much about other people's feelings, especially now since I have a baby to look after and his health comes before anyone's feelings. And I was also in someone else's house so I didn't feel like I had the right to say anything. But now I do.

Well I wanted to talk about their smoking around us and honestly if they invite us over how they can respect me as a new mother and what I say with my child. I don't care if that sounds rude but that's what I want. If they don't agree with that, they can visit us at our place or not see us at all. My SO said they'd never go for sitting down and talking about it, especially their smoking. Which I agree because they wouldn't even stop smoking around me when I was pregnant.

I haven't seen them in 2 weeks (my SO works at the same company they do so he sees them once in awhile). Tonight was my BILs birthday but they went out to eat and we don't have the money for it so we didn't go. (though my SO wanted to go even if it left us hurting a bit... Though he didn't think it would hurt us. I disagree especially since I'm the one that handles the finances.)

They asked if my son and I want to go over there tomorrow when my SO goes off to work for a half day with his dad in the morning to hang out with my MIL and BIL and if I need to sleep in the morning she can watch him... I don't want to go over. Not until we talk at least. I don't know if I should just call my MIL and tell her I'd like to discuss some things with her and my FIL or what. But I don't want my son to be present at their house before we've talked.

I've asked for advice on this before and people have said that asking them to sit down to talk about what they do in their house is rude but I feel like smoking around, first, a pregnant woman who asked not to be smoked around is rude and, now, an infant who shouldn't be smoked around & doesn't even have a say, is extremely rude and harmful to his well being.

What do you guys think?