I know EXACTLY how you feel.
I'm really the only overweight one on my mom's side, so it's really easy for them to say, "Oh, your sister has Pizza Hut night, so we're buying pizza" or that we're going to this local restaurant here that has majority fatty foods (no healthy selection markings or anything!)
And then on my dad's side, everyone's overweight, but none of them care! It's really frustrating; it's like I fit in with neither side of my family.
Don't stress too much though! Everyone has people in their lives who do things like this. With my mom, she always says everything's okay in moderation, but if I'm at a point where my "moderation button" is broken, it would be nice for her to cut back on the junk food. Just try to have a one to one with him and see if he can limit himself to buying things only for him? You're in control of yourself, not him. And don't worry, we're all here for you!