Smoker parents and newborn

I’ve already told my parents who are visiting for a month that if they want to hold my son, they need to change their clothes after they smoke. They smoke often and even though they smoke outside they smell really bad. I brought it up again and my mom got offended. I don’t want my son breathing in the third hand smoke and smelling like cigarettes. He already smelt like cigarettes and I bathed him right away. It’s to the point where I try to avoid letting my parents hold him. I went to the washroom just now and came to my dad holding him right after he came in for a cigarette. It’s bad enough that I have to smell it and I have asthma mainly due to my mom smoking when pregnant and my parents smoking in the house. 😬 I don’t even hug them because they smell and it can trigger an attack or headache. I’m at a loss at what to do. They leave on the 28th back to Canada and probably won’t see us for a few years. But I still don’t want my son’s little lungs and skin exposed.