Raising your brother and disciplining him should not be your responsibility. Your only role with your brother is that of a sister. Unless there is a logical explanation to the contrary, your brother's behavioral issues is your parents' responsibility.
I agree with Mark. Why are you "co parenting" your brother?
It sounds like the family structure is really so difficult that it might explain his poor behavior. Unless your parents are deceased I can't imagine a positive reason why you are "co parenting".
Especially if "every one of us in the family" is jumping in and trying to parent him. If your parents are deceased, or out of the picture entirely, he should be living in a situation where only one or two people has parental authority, and they should (hopefully) be someone experienced at raising kids. Do you have an aunt or uncle who could step in?
So what can you or your family do? I think that was the question.
First, someone who has the authority should contact the school and see about testing for ADHD or anything else that could be causing this behavior.
Since this has been going on for some time, and I assume he is at the same school - they should be quite willing to do so.
Second, he is really still young to be punished for what he is doing at school. His misbehavior at school needs to be dealt with immediately by the school. And at home he should be punished for only those things that he does at home. If he was sent home, then he was suspended. And a school can only do that so many times legally. I am pretty sure that his teacher wants some help, and thus should be open to recommend testing.
At home. Definitely make sure that he is getting a good nights sleep. And that involves going to bed at the same time every night. Tons of studies have been done that prove lack of sleep and inconsistent bed times can be major causes of problems the next day.
Get the book, "SOS Help for Parents," by Lynn Clark. Found here - http://www.amazon.com/SOS-Help-Parents-Third-Edition/dp/0935111212
Follow its directions. Essentially, the rules for behavior modification are that there must be immediate, short, consistent consequences. Do not expect overnight miracles. It has taken him awhile to get to this point and it will take a while to relearn control. SOS will show you how to work this system with him.