I am coming from a background of having an almost 16 year old step-son who has Bipolar Disorder and all of the symptoms you describe above plus more. Our step-son has been in therapy since he was about 6. And we have been going to family therapy with him since that time as well. One of the most important things everyone can do is to find out why. We all think we know why our troubled child acts out the way he does but often we are wrong. I'm not saying this will be an easy task, because often the children themselves does not know why they do what they do. Still, every time there is an acting- out, the question needs to be asked. Why did you do that? Why are your grades falling? Even if the child answers with the dreaded "I dunno", you have planted a seed to get the child to do some introspective thinking. Of course, I am going to tell you that I would recommend him to go to therapy, as well as his parents. I would also be questioning the diagnosis. Many mental illnesses have similar symptoms. Misdiagnosis is common and really complicates the therapeutic process. Medications can cause symptoms that seem to prop up the given diagnosis when they may only be side effects.
As his sister, I would recommend that you carve out regular time to spend with him. Right now, he is probably only getting negative attention which is understandable but can also fuel the behavior. Everyone wants positive attention but if they can't get it they will take the negative kind every time. Since you rightly point out that it is not your place to be raising your brother, you can take on the role of a person in his life that only provides positive attention. Can you have him over one night a week for dinner? Can you ask him to come and babysit your 4 year old and then heap praise on him for being such a wonderful uncle? I am sure you will come up with many creative ideas for giving him some positive attention. Talk this over with your parents; they may be hesitant to allow this when he is grounded for some of his many misdeeds. We did the same thing with our son. But we are having to re-think everything at this point. Our son is in a residential treatment center in Florida right now following a serious suicide attempt which resulted in a coma, pneumonia, tracheotomy and rehab for a minor brain injury. His hospitalization at Children's Healthcare of Atlanta - Scottish Rite was 40 days and he has now been in a psychiatric residential program since December 20. If you care to read more about our story, we have a Care Page set up for David. Here are the instructions on how to view it.
1. Go to www.carepages.com?ipc=pinvitetemplate
2. Click "Visit a CarePage"
3. Register (first-time users only)
4. After you've registered, enter the exact CarePage Name below:
davidsimmons
Hope this helps, S.