Ultimate picky eaters?

I have a whole family of picky eaters. My husband almost always eats fast food. I don't get fast food regularly for the kids but their 4 food groups seem to consist of cereal, PB&J, pizza, and McD's. BTW the kids are 4, 6, 8, and 15. The 15 and 8yr olds will at least try it before deciding. The 6yr old will cry as soon as she sees it isn't one of the 4 food groups and the 4yr old takes his cue from her. I have stopped making more than 1 meal and told them if you dont eat said meal you dont eat. My family isn't fat but I worry if they are getting the right nutrients. I have gotten them to increase their fresh fruit intake since its summer but what do I do after this? I am a good cook but in any given meal on any given day someone doesn't like something and won't eat. This includes chicken, beef, sauce, potatoes, pasta, hot dogs, the type of jelly on the PB&J or the toppings on the pizza. Nothing seems to be a favorite for too long. Any ideas?