You will be amazed at the sense of relief you will find once they're gone; can't imagine how hard this has been on you...and you will find that the group dynamic will change for the better too when everyone else isn't having to be 'on guard' all the time. Fortunately, you have understanding parents as well...I would be ticked if my child kept coming home with bites from another child.
And, after having worked so hard to try and solve the problem, try to be guilt free (easy for me to say, huh?) in your decision.