M.M.
I do invest lots of money, time and effort to keep my boys apart - and schedule sports so they cannot move a muscle after a day is over. Those are the only things that seem to be working.
For older ones try chores or what we do is if I hear/see nasty behavior - towards the younger brother - he writes pages and pages from a book. We decide how many pages and what book. It happens usually after a warning or with a particularly nasty trick without warning. So, he has time alone, practices his penmanship, learns something new and gets out of my hair. The little guy gets a time out and he is rarely one at fault, anyway. With older kids I would suggest chores for offenses. Washing dishes, cleaning the bathroom, scrubbing the tub and washing shoes -are the few we employ.
Good luck.