The kribensis females will probably keep to different side of the tank or as far apart as the pair of rams will allow. I'd make sure you have enough caves for the females. Small clay flower pots make excellent and cheap caves. They look nice in my opinion as well. Are you looking for fish in addition to the rams and kribs? If so, I'd suggest a BN pleco or two since it's recommended to keep 1 per 20 gallons. I'd also recommend two different schools of fish. One would be either neons or cardinals and the other something like rummynose tetras, black neons, rasboras, etc. Then I'd get 7 or so hatchetfish for the upper level of the tank. You could even add 4 angelfish if you wanted. You have many options with a 55g. Look into apistos as well unless you are set on rams and kribs. A trio of apistos would go well but only if you get rid of the kribs or rams. A half dozen or more cories could go nicely in the bottom of the tank as well.