Male trying to be dominant?

My big cuddly boy Rhett, 1-1/2 year old, came here with a litter
mate, a female, in Nov 2004. They were tiny kittens then. Now this
boy has grown much larger than the two older cats, and they play
really rough with each other. They all seem very evenly matched, and
even Bonnie, who I worried was to timid for bully Shamrock, has
proven to be rough with her play, too. Lately, whenever Rhett plays
with either of the two older cats, he lets out a howl that would wake
the dead. I go to make sure no one is hurt (the two older males have
each had to have vet treatment for their play-fights; Shamrock for an
eye that got ripped by a claw, and recently Rhett for his lip that
got ripped) so I know they *do* play rough enough to hurt each other
if it gets out of hand. Of the four, I can keep 3 sets of claws
trimmed to minimize injuries, but Bonnie, being a former feral, still
won't allow me to handle her to clip her claws. She seems to be the
one inflicting injury lately. Or, it SOUNDS like she is judging by
Rhett's screaming. Could his screams just be to tell her to "jump
back"? I checked him out after he screamed tonight, but he didn't
have any injuries this time. I've never heard a howl come out of a
cat like I heard tonight!

--
Cheryl