Males are kept by themselves and Females can be kept in small groups. Some females may be more agressive than others and may have to be treated like a male, but most can be kept 2-4 per 20g tank, maybe even 5-6 but that would be pushing it.
right my males each have their own cage. We have 2 females in one cage and the other two have their own cage. I was thinking about combining females for a little while to cut down on cage space.
Try it out. If they dont get along you can mix and match them. You may be able to get 4 in one 20L but it would require several hiding spots and daily cleaning.
I don't find that they are terribly social. Having them all in one cage would be less cages to clean. It isn't likely that I would do it permanently but for while we are out of town etc.. it is easier for someone to take care of fewer cages.