If you really want to go hardcore and focus on breeding certain species i'd setup a species tank. That way they can be at peace and breed easier, you could control the enviornment easier, and you could save a lot more babies.
Whats your pH at? I've heard raising that to rift lake level helps. Make sure you have a good Male/Female ratio as well.
One other major thing that can play a role is the diet. Another reason why a species tank would be great. You could feed your peacocks some brine shrimp, blood worms, krill (Though not a lot, can cause bloat even in peacocks) without the Mbuna getting much of it. Something like bloodworms only once a week or so might work. From my experience, Mbuna will out compete peacocks for food all the time...seperating them may be the best way to watch their diet.
I see you only have 2 peacocks. Try and get 1-2 more females. Peacocks like breeding in trios or groups with 1 male and a few females. This also cuts down on his aggression and beating of 1 female and spreads it out a little.