non smoker living with smokers…

i live with my bfs parents and we have a 3 month old, we are upstairs while his parents room is in the basement. they seem to think it’s okay to smoke in their room with a baby in the house and also their grandson who is a 3 year old who has bad asthma(not my kid) although i am aware it isn’t my household and i don’t have a say plus there’s no telling them anything because they’ve had 5 kids and “everything was fine”… can someone suggest how i can cover the vent where i smell smoke from. humidifier doesn’t really help and i hate that me and my baby have to smell this. i was looking at vent covers on amazon but i wasn’t sure if they would even work. i also think it could be my ac that i need to cover since that’s an additional vent to any outdoor odors. thank you in advance.