J.R.
I would look into getting a more thorough evaluation of them and maybe look into getting some medication to help control their anger. Also look into natural methods. I know you didn't mention ADHD but I recently read some articles about the fact that most kids with ADHD are deficient in magnesium. Giving them a magnesium and B6 supplement had a calming effect and reduced hyperactivity. It can't hurt to try. Click on this link and go down to causes:
http://en.wikipedia.org/wiki/Adhd and it talks about it.
I have a foster child that's been with us for almost a year now and he's got a lot of challenging behavoiral challenges as well. I find that the more one on one time he gets, the better his behavior. I know it's hard with 3 kids (I have 4), but it might help.
Good luck and keep your chin up. Hopefully you'll get them figured out soon, keep at it and don't give up. It's better to get it under control while they are still young instead of waiting until they are old enough to kick you butt :o) Then it's impossible.
J.