You can lead a horse to water...but you can't make them drink.
I know. Myself, my son and my daughter are all celiacs, and I see it in my family members as well. I've told them about the disease, sent them letters and emails...now I just have to drop it, and let them deal with it.
I know it's hard, it's frustrating, but if you push it, they will be like bulls...or nanny goats...they will not accept it. They may never accept it. But by presenting it to them in a calm way, with correct information is all you can do. And when you see them, perhaps offer them something gluten free. But don't be a nag. No one listens to nags.
Sorry if I sound harsh...but lets face it...how would you react? Tina