runner dad,
A young man who is a junior in college (so he's at least 20 unless he's young for his class) who is "brutal" to his younger brother has some serious problems. I'm being serious here. Lord knows that college kids have lots of growing up to do, but the sibling rilvary to the point of him being "brutal" to his younger brother should have passed by now.
You need to have a man to man talk with him. "It's time to grow up JUNIOR! You start behaving like a civil person toward your brother, or I'm cutting you out of the WILL. You are behind where you should be with your maturity. Stop it or I'll break off your college funding. You behavior is unacceptable."
Maybe you've never spoken to him like that. Maybe you have. If you have and he still behaves like that, then it's time to levy some serious punishment -- that's usually in the form of money for a 20-year-old. Don't pay for anything. Make him pay rent while he's home. Stop paying for college. Make sure he knows that you're serious. Tell him that even though it might amaze him that you love that other son of yours and you will NOT see that kind of "brutal" behavior from your oldest without reprecussions. Have the balls to do it. Your eldest son just needs to grow up. He needs your kick in the pants to do it.