I thankfully live in a smoke-free home, but if I didn't, I would beg the smoker(s) to please take it outside. Second-hand smoke is not good for a pregnant woman to be around.
My inlaws are smokers, and I do not allow them to smoke around me or my daughter. Even if it's their own home, I ask them to respect my child (and my wishes) enough not to do it in her presence.
As for quitting, it's not easy. It'll probably be one of the hardest things you ever do, and your chances of relapsing are huge. But quitting as soon as possible is the best gift you can give your unborn baby. It's one of a large number of things we mothers need to sacrifice for our children's health.