What size is your tank? The 90
gal or 120
gal? Take the measurements and put them into the calculator at the link at the top of the page. It will tell you how big the tank is.
What kind of peacocks are they? You can mix the Mbuna's and the Peacocks. I have them mixed. But you have to watch what you put together.
I feed a mixture of foods: Pellets, flake, peas, zuc, and so on. The tank size being large compared to the fish is a good thing, you won't have any adverse effects because of it. Pretty soon you'll have it fully stocked and will be wishing you had a larger one.
Don't feed them tomorrow, let them go about 48 hours without food. Then feed and see how they do.
BTW, what are you current tank paramters? (Ammonia, Nitrite, Nitrate, pH, temp) How long has the tank been setup?