Ugh, that pisses me off. I used to smoke, but I was extremely considerate of non-smokers and would never light up around them. I also didn't smoke in my car or house though.
I hate the "well I turned out fine so you should be okay" argument. Yeah, my mom smoked when she pregnant with me too and I was fine, but that doesn't mean sh!t. And the fact that the smell makes you feel sick should be enough for your DH's family to be considerate and step outside to smoke.
If your DH fails to see the problem, then maybe you're just going to have to be a b!tch and stay away from his family. There's no point in continuing to make yourself feel sick and uncomfortable.