You are definitely not a bad daughter! Sorry you've had such a rough time with them visiting.
My only advice would really be to just sit down with him and have a nice gentle (but firm) talk with him and just make sure he knows that you want him to be around to see grandchildren and things like that, and if he won't do it for himself, think of all the people that love him (including you) and do it for them. Maybe if you can make your mom really understand this too she'll keep on him better back at home. It's hard to change people's habits when they have had them for so so long. But it doesn't hurt to try!
And maybe you could get him to realize that he doesn't have to give up things he loves, they could have turkey burgers instead of hamburgers, and healthier cookies and cakes, and things like that.
I'm sorry I don't have better advice for you but I don't think you should give up because you love him and you want what's best for him. Big big big hugs and take care! How have you been feeling by the way?