Wa alaikum salam,
Your fasting would be valid as you are not smoking yourself. Simply don’t join them when they smoke.

Assalamu alaikum. I intend to fast this ramadan and i live with my mum and dad and don’t have money to move elsewhere. My dad smokes in the house and is not well he has been told not to but he still does it. Also other people may smoke in our house who do not listen so i was concerned that if i could smell cigarette smoke that my fast would be broken but i don’t know what to do. What am i to do?