Mother in law smoke

So my mil smokes ALOT and so does her husband. Since they live alone they also smoke in the house. . . Im 34 weeks and starting to think about how to tell them or how to respond to them when that ask why I'm not going over to visit ( my husband is a mamas boy which I don't mind, he takes my side for mostly everything ) when the baby is here . . .recently we went to go pick his mom up from her house to go out shopping and he went in there for less then 10 min and when he came back in the car he smelled like smoke all ready . . . I'm not taking my baby to their house till shes older and her lungs are developed a bit more . . . Since it should be cold when my baby is born they can't even open a window . . . Is that mean on my side ? I don't know how to explain it to her