Help with 4 yr old!!

I need advice and fast. My 4 yo DS is out of control. He hits, bites (hasn't done this in a while though, Fingers crossed), throws anything he can get his hands on, screaches at the top of his lungs and more. He does all this when he is told "No" or when DP and I tell him "It's not to hit". Sometimes big brother teases him and the war begins. Because DS4 cannot express his feelings in words to well, he reacts in a violent way. This is all done to his older brother and at times me. I've tried time-outs but they don't seem to work. Maybe I'm using them too much? I've tried paying no attention to him when he hurts big brother (all my attention went on big brother), tries talking, yelling (that gets nowhere). Now I'm out of ideas on what to do. DS is as good as gold when big brother is at school, but the moment big brother walks in that door all hell breaks loose. Could there be jealousy here?

I don't know what to do anymore... :