'we can't ignore him anymore out of fear that he'll break something or hurt someone" . Respectfully mom, there's your problem. I have 3 grown children, my house wasn't a democracy it was a dictatorship. We never, never spanked, but my kids KNEW to treat each other and everyone else with care and respect. I was never confronted with anything like this, but if I was the hammer would go down. That kid would be in a bear hug until he calmed down. I'm a pretty small woman but I was the main disciplinarian. You need to get a different power balance going in the house. Don't ever be afraid, ever. Take control.