Unless you control the cooking and the shopping you can't get them to eat better. They have to want to eat better. Nagging will only make it worse. You can suggest you'd like to eat better, but, at the end of the day, if you're not the one prearing and buying the food, they'll continue to eat what they like. I'd suggest focusing on yourself first, and maybe if they see you making positve changes, they'll follow suit. That will mean shopping and cooking for yourself, though, most likely.