You COULD divide the 5 gallon for two females, but because females tend to be so much spunkier and more active with their shorter fins, giving just one female the whole tank would probably be a little more ideal.
If you do decide to go ahead and divide, or if you have the females already, make your own divider. Its a lot easier, cheaper, and more stable then those store bought ones.
I use this method for all my dividers, except I use two sheets of craft mesh and double up, then do a little bit of trimming and more exact fitting so the divider fits snugly without bending. This seems to work very well for me.....makes the divider a little more straight and stable, plus is less see-through.
Females are VERY good little jumpers, so you'll want your divider to come nice and high, almost touching/touching the hood if you can. You may want to put up a jump guard(just a long piece of craft mesh laying flat over the length of the divider that extends an inch or two over each section to help stop them from jumping over)as well to be safe.