I'm afraid that I agree with Stephanie, it is his house. If you were actually living there, then yes, it would be nice if he would go gluten-free, but many celiacs live (safely) in homes that are not gluten-free. It would be nice if he was gluten free, but you are now only a visitor and I think it is too much to expect him to go gluten-free for a frequent visitor - even if it is his daughter.
It sounds like the butter is the main issue. Perhaps you could buy some butter for them, to be used only for your dishes. Put it in a tupperware container and hide it in the back of the fridge, or even freezer, where he won't touch it. I'm sure that your mom could make sure pans and pots are clean before using them, and if you question the cleanliness of the utensils (my utensil drawer collects crumbs) just wask them off before using them, and have your mom wash them before using them to prepare your food.
If all that doesn't work, you'll have to have them over to eat at your home instead, or bring your own food when you visit. Better yet, bring gluten-free food to share.