how is it harming your skin and lungs (body overall) if your family members smoke outside but stink in the house?

Secondhand smoke is secondhand smoke, even if you’re not seeing billows of it. If you can smell the smoke, it’s still there. Now, the concentration of it is likely significantly diminished, so it’s probably not nearly as harmful as someone smoking indoors. No real way to measure just how much the difference in effects are, though.