You are in luck- looks like you have two females already. Rams can be difficult to sex- especially the long fins and baloons, so take my ID with a grain of salt. I can't be 100% positive, but I'd put money on it.
The standard is almost certainly a female- see how the very farthest back end of her dorsal fin does not come past the beginning of her cadual (tail) fin? On a male it will be longer. The ballons, since they are smooshed up, its kinda hard to tell, but it appears as if her belly is pink (unless that's just the camera) a sure sign she is a female.
The good thing about having two females already is that if you add two more- the absolute worst case scenerio is you end up with two males in a 55 gallon- still plenty of room for territory. I'd shoot for one male and one more female. Even though there is enough space for two males to co-exist, each with their own two feet of tank space- undoubtedly they're both going to want the center 2 feet.