How can you tell the gender of a leopard gecko? They live together?

Answer 1

Once they mature, it's easy to tell, because a male will have a "bulge" behind the vent and preanal pores. See this link for a photo: http://www.repticzone.com/articles/sexingleopardgeckos.html When they're juveniles, you can't tell them apart visually.

Only one male can be kept in an enclosure, but you can keep any number of females by themselves or with a male.

Answer 2

You can only tell gender once they are around 6 months old unless you are really experienced. Males will have a bulge at the base of the tail and they will have pores in the shape of V right above their cloaca.

2 females can live together as long as they have enough room. 2 males will fight. A male and female kept together will breed too early and the female will die young due to not being mature when being bred. When in doubt, it is best to keep them seperate.