Hi,
From the pictures I would say that (like others):
Pic 2: Red Zebra (Metriclima Esthrea)
Pic 3: Red Zebra
Pic 4: Red Zebra & Yellow Lab
Pic 5: Yellow Lab
Pic 6: P. Socolofi
Pic 7: JD
As for the fish, I do not think the Lab with the black side marking is a cross or at least not a recent one. Yellow labs are one of the most popular Mbuna cichlids. This means that they have been inter-bred alot, there is not many wild caught yellow labs around. The black muddy stribes are seen on many yellow labs, and the breeder will have to be very dilligent to maintain only a pure yellow which has not been the case for many years.
The "peach" fish you are referring to are in my opinion also a red zebra, usually the males will be bright blue and the females deep orange but it is not uncommon that a male can have a peach color, when it grows older you are likely to see a blue "hue" when it is in full color, they can at times seem almost white. From the picture the body shape seem to be a little off but this can also depend on where in the lake it is from, so from the picture I will say Red Zebra male.
I think it is hard to call the P. Socolofi based on the picture, but you have seen it "live", so you know best. They also come in many variations.
You also ask for opinions about you tank and set up. So here goes:
1. Get rid of the JD, it does not thrive under the same conditions (PH / Plants etc.) nor does it eat the same food as the Mbunas.
2. Lake malawi has no significant plant life, and the Mbuna section of the lake is the coastal area where there is nothing but sand and rock. The picture shows the Mbunas natural habitat.
Therefore I would suggest that you should remove your plants and build a rock formations in your tank with alot of hide-outs and passages for the fish to "claim" and use when fleeing and hiding from agression, more pottery could also do the trick. You should also remove and natural roots and wood since they will lower the PH and this is not what you want in an Mbuna tank. The PH in their natural habitat is 8+.
I would also change the substrate for sand (approx. an inch worth thruout the tank). The Mbunas use the sand to clear thier gills of parasites, and they just love digging to clear the breeding area, the males will do this with a passion.
3. As to your population, there is a lot of debate around overstocking for Mbuna. The Mbuna does not "prefer" an overstocked tank and they can successfully be kept without overstocking, but that requires that you selectively choose the "least" agressive of the Mbuna, and preferrably let them grow up together.
I would say you should supplemet your current population, so you end up with something like:
1, 4 - Yellow Labs
1, 4 - Red Zebra
You should not try to introduce more Mbuna types in a tank this size, the Red Zebra and the Yellow Lab are some of the more peaceful Mbunas and with plenty of rocks it should work fine. The number will not act as an agression inhibiter, but it will make sure that there more fish to spread the agression on so that no single individual is picked on constantly.
4. In my opinion the tank is a little small for Mbunas, but many people have successfully kept them in tanks of this size and even smaller so...
5. I am not familiar with the specs of your canister, but Mbunas love cirulation in the water, again living in a coastal area there is alot of movement in the water. Again there is some debate around how much circulation, the advise you will find ranges from 3-10 times the tank size per hour, for a 55g tank this would mean a pump capacity of 150gph+.
I found the following picture on searching for 55G Mbuna tanks, I think you should go for something in that direction:
