Let's face it, your family does not always want to eat the way you do. Regardless, I try very hard to inspire healthy eating habits in my family. Sometimes I even go as far as tricking them. If they don't know what's in it, they don't complain. The minute I tell them I substituted something for a healthy ingredient they automatically say, "Yuck! It's disgusting." So, it's simple: DO NOT TELL THEM!
For years now, I have been substituting plain fat-free yogurt for mayo. You can make the switch gradually by mixing half mayo and half yogurt in your tuna, or whatever else in which you typically add mayo. Add some salt and pepper, a little lemon juice, and pickle relish (or whatever your family likes). Eventually, use only yogurt. The same thing goes for mashed potatoes: use half cauliflower, half potatoes, and add some grated cheddar cheese and/or roasted garlic. Eventually, just use cauliflower. They'll never know! :)
Here's to a healthy family...cheers!