I make reference to your question in another thread about "Old Man"

pride. Well, this is possibly the negative side of this situation. Those more senior to us sometimes believe we are ****y know-it-alls that persist in telling them how to live their lives, etc.
I have this same situation with my parents and two younger brothers.
All I can say is explain in terms of what they deserve not what they need to do. ** You know Dad, you work hard and you deserve to relax. Hey Dad, I've found that eating 5 to 6 smaller meals makes a difference in my energy and physical comfort. Nothing like have energy throughout the day!**
Four ideas:
(1) Be a role model and when the opportunity comes help them move forward with honest excitement. Be there as long as it takes.
(2) Think in terms of lifestyle change. Replacing the sofa with easy talking and walking then slowlu improve from that point.
(3) When it comes to food, think taste and presentation!!! Expensive restaurants charge ungodly sums of money because the make the food look and taste great!!
(4) Gather / develop great recipes! I purchased Eating for Life because it provides a great baseline of recipes that are nutritious. My wife and I have invited friends and family over to eat using some of our favorite recipes. When they learn that nutrition can look and taste great they open their minds. Two of the six have begun to exercise and eat better.
Good Luck!!