No. The majority of both West African and SA cichlids come from generally soft, acidic waters. Ya wanna get down to the exact water parameters of any given biotope, there will be differences. But overall the water conditions and biotopes they inhabit in the wild are very similar. Kribs are an anomaly as they range from the soft acidic, upper waters through brackish coastal waters. They will do fine in either. Now, add that fish that have been captive raised in non-native waters, as both of these fish have been for many generations, become acclimated and nearly naturalized to those waters, the fish are much more adaptable to a wider range of water parameters than their WC cousins and will be quite fine in parameters varying a bit from their native waters. Now I can respect your opinion that the fish shouldn't be mixed, but it is far from fact. Obviously the ram and krib are doing quite well.
Now you're throwing multies in there, as well, which is an entirely different scenario. They are not West African, they are a lamprologine cichlid from Lake Tanganyika, and they will do much better in different water conditions, namely harder water with a higher pH. You've changed the condition ya initially argued to encompass a fish that is outside of the original parameters you stated, namely West African riverine cichlids. Multies are irrelevant to your initial statement as they are not a West African riverine cichlid, and adding them to the mix is a lame ad hoc argument.
IME, the only way I would wanna do three apistos in a 20 long is if you have a harem situation: a male and a coupla females. Even in the absence of females, males can be a little hard on each other. In addition, there is no need to limit a shellie tank to two individuals. A colony of eight to ten shell-dwelling, somewhat social multies in a 20 long makes for a very interesting set-up.
As it stands, sharmz's fish are doing fine in the tank as it is now, so why suggest that she break up the tank? If it ain't broke, and she's happy with it, don't fix it.
WYite