Accute Anger

My grandson who is now 13 has had behavior problems since daycare.  He has seen doctors and has been tested for ADD etc. they say he does not have this problem,  He still wets the bed and has been to see specialist on that problem.  The family went to counseling and again that only helps if the person wants help.  He and his older sister (16) have fought since day one and still fight all the time and now he is picking on his yournger sister (7) the same way.  He is very very aggressive has trouble in school with the agressiveness because he has a very short wick and flys off the handle at a drop of a hat.  To top all this him mom died a year ago with very fast spreading cancer did not have time to really prepair the kids for it and now he has that anger on top of every thing else. One moment he is the most loveable child the next he turns into this angry defiant monster. I am so afraid of what is going to happen to him because of this, his father is at witts end as are both sets of grandparents.  Does anger run in famlies?  My father, brother and my husbands brother all had really bad tempers.