Second hand smoking

Hi, in my last recent scan was told my baby has black image in the heart through the scan. But dr haven't confirm if its a risk. Since im pregnant, my sister and her boyfriend has been smoking outside of the house despite me telling them to go far away to smoke. Im okay with it but im more worried about my unborn child even if my baby doesn't have any issues. I mean, I've become super protective of my baby since i was pregnant as it been hard to conceive took me almost a 2 yrs. I will do anything just to keep my baby safe and healthy. What should i do? Im so stress at home. I feel like they just don't care.