Offer variety and don't be afraid to offer something that he doesn't like, a couple weeks later, either prepared differently or the same. Make sure that every meal he has to try, at least a small bite-size portion. And don't get in the habit of making separate meals for him because he "won't eat". Teaching children to learn to eat "what's on the menu" is so important. Otherwise you will be preparing many different meals. Don't keep offering chicken nuggets and taco meat. Try some chicken tacos, using chicken breast, seasoned and tell him he has to put at least 2 ingredients, plus the tortilla, on his taco (i.e. lettuce, tomato, cheese, salsa, beans, or whatever else is being served)
Have him help you cook and prepare meals too. Try making quesadillas or fajitas w/ chicken and cheese. Those are fun for kids to make. If he doesn't like fruit, try serving it up in a smoothie w/ a little juice and yogurt, if that is something that he can eat. If he walks away hungry, don't offer a snack or dessert at a later time. He will get in that habit. I know it's hard to see your child hungry but, if he can learn not to eat between meals AND, once he learns that there won't be any more offered, you can work to break this habit.
Has he had a severe reaction to eggs, other than hives, like a breathing concern? Could food just make him nervous, thinking it might happen again?
Also, kids need to learn that the dinner table is much more than just serving food. Give them a reason to want to be there too. Make sure you are asking them about their day and they are asking you about yours. Find a funny story to share with them or ask them a thinking question, "If you could go anywhere in the world for vacation....?" "What was the BEST present you ever received...?" etc... You don't want your dinner table to ever be a battleground. Good conversation takes some of the focus off of him and spreads it around the family. I'm sure your oldest (and best eater) will become a great example of a kid who can eat....AND...share stories!
Good luck.
EDIT: I just wanted to add...once the conversation gets rolling, it's those moments that you can start telling your 4 year old, "Oh, I REALLY want to hear what you have to say, BUT you have to eat something first!"... For a kid to have the center stage in a conversation!!!! They don't want to be left out. Positive reinforcement when he does eat!