They don't get very big, about 2-2.5 inches. It's just that 10 gallons is too tight of quarters for more than one.
You can --- rams actually kinda easy, when you look at the dorsal fin, the first few rays will stick up a little higher than the rest, like a mohawk, that's a male.
Also, the females have blue irridescence in the black dot on their side, as where the male doesn't. This is something that you have to be looking for and it's not easy to determine unless you have a female with a lot of "dots" in her black spot. The spot is easy to identify, it's big and black on the fishes side.
Other than those little differences, they are identical.
Unfortunately for the puffer it's a design or stripe on thier belly that the females have and I've got no idea what it is. I've heard of people keeping two in a ten gallon, but after thinking on that over night, I would ditch the 2 females idea and go with a pair, a male and a female. Who knows, they may breed! I'll have to look around and find the sexing technique on them, it's easy I just don'e remember what the marking is that distinguishes them.