These are all very real issues that most gluten free house holds face. I can completely understand where you are coming from. You have to remember that your duty is to yourself and your children first.
Other family members are responsible for their own health. All you can do is inform them of your situation and the potential for them to benefit from being gluten free. If they don't accept this advice, it is their right. You cannot let their health burden bring you down. Your only obligation is to inform them.
If you feel like they are not trust worthy with your children, then do not let them sit for you. If you stand your ground consistently, they will come to accept it even if they don't like it.
I would recommend that you watch the following video:
It goes into the depth of this problem and what you can do.
Stick to your guns. You know in your heart what is right for you and your family.