cat is a bully

We have four amazing indoor only cats, but over the past couple of years,
one of them has really become a bully to one of our other cats. Here's
our cat family:

Brak - Male 18lb - 5y old (the bully)
Warren (Braks brother) - Male 13lb - 5y old
Kaya - Female - 7lb - 10mo
Zena - Female - 10lb - 13y

Brak is probably the best lap cat/people bather (except he can't sit still
in
your lap for more than 30 seconds at a time before he has to readjust),
but he will NOT leave Zena alone. He traps her into corners and
behind the big TV and bites at and wrestles her. She screams and
yowls, she won't fight, she rolls over on her back which makes it even
easier for Brak to assault her. As you can see, he's almost twice her
weight.

Wife has had enough and had told me one of them has to go. We love them
all, Brak and Warren were inseperable which is why we adopted them both
(though they don't seem to be now, Brak jumps on him sometimes too and
****es him off). Zena is wife's cat from before our marriage.

More living space might help the problem, but right now we simply
don't have more space to give them. They're confined to the downstairs
which gives them 3 rooms. Wife doesn't trust them upstairs (except Kaya)
as they jump into baby's crib (Kaya is small enough to squeeze under the
gate blocking off the upstairs).

The plant sprayer doesn't deter Brak at all. He hates it but even after a
year of squirting him, he won't change his behavior. When he had her
trapped behind the TV the other day, he ignored my wife yelling at him
because he knew she couldn't get to him physically. She had to find the
water bottle and spray him to get him to leave Zena alone.

I don't want to get rid of Brak or Zena, but I'm not sure what I can do
to change Brak's behavior. Wife is at home all day and says it happens
several times a day. Any help greatly appreciated.