Unless your DC are going into sheltered residential accomodation after they leave home they will need to be able to prepare food for themselves.
There are such things as raw diets, they can be vegetarian and you can incorporate what they like, you need to be flexible op.
Rather than battle with them, be positive. Start with what they WILL eat which sounds healthy to me.
Get some recipe books out ( or get them to look online) and ask them to earmark what they're interested in and jot down ingredients.
Involved them in writing a shopping list, and in the food preparation. Get them to think about alternatives if what they want is not available.
Great sources of protein are nuts and seeds which do not need to be cooked but added in to a plate of pasta and vegetables. Pasta or diced potatoes or rice or beans/ lentils or hard-boiled eggs can be mixed with mayo and other things such as soya sauce if you don't want them heating anything up, you just have to be creative.
You can eat carrots whole after you have washed them so make them staples, along with apples, bananas and tomatoes.
Add in peanuts and cashews to rice or pasta dishes and you will have a very tasty, healthy meal.
Empower your DC op to make healthy choices themselves. Then when they have got confidence they will be happy to have dinner ready for you when you get home, is what mine do, same age although mine have been happily preparing meals since they could hold a knife and fork! We used to play cafes when they were toddlers and it quickly went from play food items on a plate to real ones and would ask me what I'd like on a pretend 'menu'.
Big bags of sunflower seeds, pumpkin seeds etc are inexpensive when bought online.
Bring back the fun and take the pressure off. Good luck.