YES! Have them help you with the groceries! It's your house. Talk to them and explain what the new menu will be and their share of the expenses. And that no junk food including take-out and donuts will be allowed in your home. Organic eating is really not that expensive if it is planned well and with plenty of time. The problem i hear from you, are the poor eating habits of your daughter and her husband and the lack of self survival. I don't think you raised a self-starter. If you had, they would be living on their own.

Take control of your home and health! If they don't like it, they know where the door is.