My heart goes out to you... I sense that your situation is pretty complicated and painful, and you are doing your best to try to survive and remain in good spirits about the situation.
I think that your siblings attacking eachother physically and emotionally is a much bigger problem than simple codependency. You're right about your parents intervening... that does tend to complicate the problem. Do your parents ever fight in a similar manner?
I think it's great that you went to counseling... often, just admitting that counseling is needed is incredibly difficult. You mentioned you felt responsible for your parents fighting... do you feel responsible for your siblings as well?
I've had to play referee for my parents in the past, and it can be really painful... even though you are young and supposed to be taken care of by your parents, you feel as if the roles are reversed and you have to take care of everybody else. It was a hard thing to work through, but I did (and it was definitely worth it).
Well I want to tell you right here, right now that it's not your fault that your siblings are fighting, nor is it your responsibily to stop them. That is entirely their choice. It can be really hard, because sometimes you just wish it would STOP. But unfortunately, there's not much you can do about it, and it's not your fault. And it WON'T last forever, one day you won't have to deal with this, I promise.
Have you ever read "A Guide To Rational Living" by Albert Ellis? I think there's a lot of tools in that book that might help you get through this with your sanity. I've found it at most bookstores for about ten bucks, and you can find it at Amazon.com here:
http://www.amazon.com/exec/obidos/ASIN/ ... 80-6479804
Hope it helps! Keep your chin up.
You read this sentence thinking it might be important, but now you have discovered you were mistaken.