Make a list of your family's favorite foods, casseroles, menu items. Do you like macaroni and cheese, or the casseroles that combine chicken and a can of condensed soup and another ingredient or two? Do you like comfort foods, Mexican foods, etc? What are some simple meals you enjoy (tomato soup and grilled cheese, etc)? What are some meals you enjoy cooking or want to learn to cook?
Don't think about healthy quite yet, just get the list together.
Now look at your list. Look for ingredients like processed artificial cheese products, canned (salty, overprocessed) foods, seasoning packets, jars of pasta sauces, jarred or dried gravy or sauces, stuff like that.
Try making simple substitutions. For example, let's say your family likes spaghetti. If you buy plain ordinary spaghetti and a jar of sauce, try buying a spaghetti that has some fiber or whole grain in it. And instead of the jar, make a simple sauce by sauteeing a chopped onion and extra lean ground beef, adding a couple of cans of pure crushed tomatoes, some fresh oregano and basil. You haven't changed your menu, you've changed the ingredients to make the whole meal fresher and lighter and healthier.
You know those commercials on tv where they tell you to pour a can of soup over chicken? Get some fresh mushrooms, saute them in a little canola oil, chop them and add them to a simple homemade white sauce, made from butter, flour, and low fat milk. Now instead of the dozen or so ingredients on the can, you have 4, and you can pronounce them all. Use that to basically go with the chicken recipe from the commercial.
Try "make your own salads" where you set out bowls of salad fixings, and they can build their own. You can add grilled chicken that you cut into strips, and hard boiled eggs, for a salad with protein.
A simple white sauce is easy to make, and once you learn it, you can make Mexican cheese sauce with real cheese, and a different cheese sauce for homemade macaroni and cheese, and any flavor of soup that replaces the stuff in the cans.
Good luck!