Yes a certain amount of physical play and even fighting is normal.  However you must be firm about not letting anyone get hurt. Let the boys know that if you feel there is TOO much rough stuff happening, you will discipline whoever YOU perceive to be the offender. The kids may disagree with you as to whose fault the violence is and that is why you will want to let them know in advance that this will be YOUR call - and you are willing to make the occasional mistake if that's what it takes to uproot physical aggression in your home. Then, let them know exactly what the consequence should be. In my book Raise Your Kids without Raising Your Voice you will see a section on negative consequences that describes consequences in terms of "tickets" and "jails." Kids, like adults can "go to jail" for violent crimes. You are looking for a consequence that is a "jail-level" consequence for this particular offense. In other words, don't say that you will lose 15 minutes of computer time. Say something more like, you will lose 2 weeks of computer time each time I see you being excessively rough.  Figure out what is a meaningful "jail-level" consequence for each of the kids and discipline individually if necessary. If you pick the right consequences, hurtful behavior should be quickly eradicated.