A.
My boys are both the same way. For every meal I set a timer on the oven. After a certain amount of time, it varies by meal, when it goes off they are done. If they go to school or bed hungry it's their fault. They are slowly coming around. Kids aren't going to starve themselves. For breakfast on school days, they have 15 minutes. For lunch and dinner, they have 20 minutes.
I was a single Mom working full-time for 6 years, I know what you are going through. I try to "pick my battles" but it doesn't always work. My patience is tested everyday!!
(I also set a timer for teeth brushing. They have to brush a full 2 minutes.)
Good Luck!!!