I am really sorry to hear this Dark Rose. It could be any combination of the following factors
Not enough space
not enough fish
not enough territories
Problem is you never really know what the problem is, and having a few africans together tends to mean they get more heavily bullied... but sometimes it works out. In general africans are completely random and its just luck if it works or not. Here are my experiences
My dad had a 3x2x2, mixed mbuna and a few haps like livingstoni, complete rock wall at back, no issues for years
I had the same 3x2x2 tank and stocked it with tangynikans, lightly stocked and no issues, even got the Julidichromis to breed
switched the same 3x2x2 tank to mixed Mbuna and hap with a single large rock pile in the middle, almost up to the surface, no issues. If i remember correctly I had . N polystigma, a few M. Grashekei, L. Fuellbourni, a random hybrid, super red peacock, some yellow labs, basically a nice mix. Absolutely no issues, switched over to marine in that tank.
Few years later a tank that was around 4x12x18
2 bumblebees, 3 zebras, 3 auratus (m+f+f) a convict that refused to get caught and a thick lipped hap.
tank had a partial rock wall
Constant aggression, constant deaths and fighting and moving and adding, basically like you are having.
Now my uncle has a big 6x2x2 with over 100 fish in it. the tanks been set up for over 5 years now, some HUGE fish in there mostly fully grown.
Loads and loads of Mbuna, he scoops fry out all the time and puts them in a grow tank, a bunch of really large haps too. He has absolutely no issues, the entire back of the tank is rockwork too.
Why post all this information? Because I think I may have stumbled across something somewhat relevant. a mixed african tank should be at least 2' wide. Maybe its that wide large footprint that helps the establishment of territories and gives the fish room to escape and avoid confrontation? All he display tanks I have seen in LFS` have always been at least 2' wide and contain at least one large pile, or a large back wall of rockwork.
Whats the dimensions of your tank?