As a minimum, they will need a 4'x18" tank (preferably a tall one - 90 or 110) to themselves as the males will get 8"+ and are very aggressive. Your ratio should be somewhere around 1M/4-5F at a minimum, with no other males in the tank.
In a tank smaller than this or with a lower ratio, you may have a couple of random spawns when they are small, but this will not last and the crabro will eventually kill the females as he matures.
When you consider their size and aggression, they are the mbuna best equipped to do a lot of damage. A few years back, I had an adult male that killed several full grown haps... and there weren't even any female crabro in the tank.
Not trying to scare you away, just wanted to make you aware of how rough these fish really are.