Girlie, I am a lot like you. I have a big family, and I have a hard time keeping it together. For me, what makes it hard is that I am not super organized and the larger my family has gotten the more of a problem that is for me. This is what has helped me.
Do you sleep at night on a regular basis? I'm not being sarcastic, really. With a 2 year old it's still a toss up. Our 5 year old still has trouble sleeping through the night.
I am for doing whatever it takes to get what you need. I know a lot of people will disagree with that, but you have to do what's best for your kids, and an alert, together mommy is what is the absolute best thing for your kids. If you have to have them sleep together, sleep with you, sleep in the floor on a pallet like a pile of puppies, whatever. Just so long as they sleep and you sleep.
Do make ahead and easy meals so that you aren't spending all your time cooking. Cook three or four meals on the weekend or your day off that you can put in the freezer and use during the week on crazy days. For instance, cook three pounds of hamburger meat and split it into thirds. Turn one into spaghetti sauce, one into chilli, and one into taco meat and put up in the freezer for later in the week.
Put a large desk calendar on the wall and when you have an appointment, a bill is due, there is a school activity or event you can write it down. Put it where you always see it, like by the fridge.
Get into the habit of looking at the papers in your kid's bags, and having them doing any work they have when they get right in. Then, they do it, I sign it, we put it all right back in the bags and sit by the door. Also laying stuff out the night before.
A big dose of forgiving yourself helps. Do what you can to bring peace to yourself and your home and don't sweat the small stuff. A happy mom is way more important than a perfect one.