Hang in there, mom. I'm so sorry you're having this trouble. It sounds like you need help in the house.
I hate to harp on this right now, but you need to hear it. You HAVE to stop yelling at your kids. They won't listen to you because they don't have to. When they misbehave, physically take them to separate rooms and don't let them come out for a while. Do it every single time even if it's 30 times a day. Soon, all you'll have to do is threaten to separate them and send them to their rooms, and they will straighten up.
If they are fighting over a toy, after you've sent them to their rooms, put the toy away. If they ask where the toy went, tell them you put the toy in timeout since they wouldn't behave with it. Like being tired of being put in their rooms all the time, they will get tired of losing their favorite toys too. The only way they get them back is through good behavior.
You also need to give them positive reinforcement when they are behaving. "I like the way you boys are playing so well", "Thank you for playing quietly while I make dinner", like that.
It's okay for you to be on the couch right now rather than playing with them. You've got to keep your strength for the marathon ahead. But stop the yelling. Get up and take them to their rooms. Period.