Yeah they might be okay for a week, or two, or a month, or two.... but sooner or later you are gonna run into big problems. Trust me, the species you have now wont live in harmony. The yellow male kenyi (probebly the most aggressive) when he matures will see the other two yellow fish as a threat, and remove them from the tank the only way he knows how...
I would not even keep these species in my 90 gallon community malawi mbuna tank. They are just that aggressive.
And its false that any malawi species can be kept together as long as they are overstocked....
PLUS overstocking only works in larger tanks at least 4 feet (75 gallons and up). And by overstocking we mean 20+ fish, not 4.
Please take this adivce or you will loose some fish. They are really tricky to stock. I would remove all your fish and get some yellow labs, acei, or rusty cichlids. Those are less agressive species that fare better in smaller tanks. Even the 40 gallon is going to be too small for any of the fish you have now, unless they are by themselves.
Also, while having several females to one male is advised, its several females and one male of the
same species.... just keeping a bunch of females of different species together kinda defeats the purpose... because part of the reason is to prevetn hybridization. And a male will treat each of those females differently if they do not look the same.
Try having a look at:
http://www.malawimayhem.com. I would suggest this to you, and I know you can do what you want but I will try: Is it possible for you to put your oscar in the 135 gallon (which he'll eventually need) and put the africans in the 55? At least that way the tank is big enough for you to have around 10 fish, which is not overstocking but will help a lot more with aggression. Although, you'd probebly still have to take back the kenyi.
HTH
-Diana