He has a case of ADHD, with a severe temper...All he talks about when he's mad is how he'll kill you...
First - the bad news: You have a serious situation here that is going to get much worse.
Second the "good" news: It may get better for everyone if you are able to get your brother into treatment.
I'm not a doctor, and even if I was I would not presume to diagnose your brother over the internet.
However...From what you are describing, your brother MAY be suffering from the onset of bipolar disorder or "manic-depression".
This is a very real brain disorder caused by an inherited chemical imbalance in the brain (despite what anyone may try to tell you). It isn't the result of bad parenting, nor is it just your brother trying to be a 16-year-old pain in the ass.
You say he is already on meds. Very likely they are the wrong kind. Often, early-onset bipolar disorder is mis-diagnosed as ADHD. The meds he is taking for ADHD could quite possibly make his mania WORSE.
My son went through this and it became a nightmare that lasted nearly 15 years until he finally got on the right meds and stayed on them. There is no cure.
You will be doing your brother, your mother, yourself, and the rest of your family a tremendous service if you are able to get in touch with NAMI (National Alliance for the Mentally Ill).
Please click on this link and at least inform yourself:
http://www.nami.org/
You can read about bipolar disorder and get a pretty good idea whether his behaviour fits the criteria.
At this link:
http://www.nami.org/Template.cfm?Se...ail.cfm&localID=0000150514&fromHL=no&state=IA
You will find a support group near you that can give you all kinds of resources to help your brother and your family.
God bless you - You'll need it.