I have that kind of family too (so glad my in-laws are awesome!)...but mine are supportive of my Celiac disease. But still, over the years I've just learned to set my limits with them. Don't let them walk all over you--especially when it comes to your health. I don't lie to my family anymore when they try to be controlling about what I do. I now tell them straight to their faces what I not willing to do and that's that. I say absolutely lie if you have to, but I think it's better to stand up to them and just say no. My family members would have tantrums and make threats if I said no and didn't offer a reason. So I figured, ok, I'll say a straight up no, wait for the tantrum and wait for it to pass. Didn't budge ever, and never will. After a while I said no to them just because I could. It's great having freedom to choose and being healthy. :-D
I'm sorry your family is the same. It's so frustrating. I'm getting pretty good at saying no, but this one dinner they're just adamant about, and I couldn't find any way to get them to let it go without lying. It's going to take a while for them to really understand my limits.