I have raised several kids with major eating issues - foster and bio-kids, autism, sensory issues, picky eaters, anorexia, trauma history including serious neglect in the realm of food, aversions of all sorts, extreme overeating and food-hoarding - you name it. Also some pretty horrible table manners, no idea how to act in a restaurant, etc. I have been pretty low-key about is all. The following is the general approach that worked with everyone (I had up to 6 kids in my home at a time, and would have gone nuts with different meals/plans for each!) It took me some time to let go of my notions about nutrition and "clean your plate" attitudes. Rather than balanced meals, I aimed for balanced months - and I did give them gummi vitamins. I think this was more for my guilt than their nutrition!
There was ALWAYS a bowl of fresh fruit on the counter. Anyone was welcome to all they wanted, any time, no need to ask. Same with a basket of granola bars. There were often other snack choices - carrots and ranch, popcorn, cheese and crackers, hard-boiled eggs. Again, these were free-range.
For dinner, I cooked fairly healthy but not too strange meals. Homemade macaroni and cheese, maybe with ham and/or broccoli in it, or spaghetti with meat/tomato sauce. Asian style stir fry with rice. Hearty soups and stews. Things like that, lots of one-dish meals, sometimes added a salad. Everybody was welcome to either eat what I cooked, or fix themselves a peanut butter and jelly sandwich. Or eat fruit and granola bars. Or not - it was OK to just hang out at the table.
Breakfast was at school on weekdays, but on weekends or holidays, I would make oatmeal or biscuits, and have out a variety of condiments/toppings, and everyone served themselves. Butter, maple syrup, fresh or dried fruit or berries, cheese, nuts, whatever came to mind. The kids loved "inventing" their own recipes.
Dinnertime was at least as much a social event as a nutritional one. Pleasant conversation, planning for tomorrow, games, jokes, and silliness. It was often the only time we all sat down together, and everyone wanted to be there. We didn't have the competition of TV or electronics, and everyone seemed more than happy to interrupt whatever else they were doing to join. If someone had chosen to continue playing instead (I always gave a 10 minute warning before I served), I would have just looked quizzically, maybe asked, "Really?" and let them choose. But I don't remember that ever happening.
I never bought food I didn't want to have them eat. If I bought or made popsicles or cookies for example, it would be for an occasion, expected to be finished in an afternoon. Or I occasionally baked a pie, or bought ice cream. But I never kept much sweets in the house. Same with chips and foods like that - maybe for a picnic, but I didn't normally have them around.
Eventually, even the pickiest eaters got a bit more adventurous. The kids who had experienced severe hunger came to trust that food would always be plentiful. My boy with serious sensory issues now, at 17, eats everything except mashed potatoes (or food of that consistency and texture) - his favorite treat is sushi. This is the kid I swear lived on nothing but popcorn for 3 or 4 years!
I agree with those above who suggest relaxing about the eating altogether. It really will sort itself out. I love the picture of the 20 year old running lapps around the table with her date at the romantic restaurant. I will chuckle about that all night!