By far the best way to keep gerbils is in a breeding pair. They will remain together for life and the male will assist in rearing the young. They may produce up to 9 litters in their life time. However, you must be sure that you can handle so many young gerbils, because if you separate the pair they cannot later be reintroduced nor introduced to new companions.

Gerbils are extremely territorial and will not tolerate strangers. If you do not wish to keep a breeding pair then a two or three females will live happily together. In general, keeping two males together is not a good idea, but may often be better than subjecting them to a life of solitude. If the fighting does not get bad enough that blood is shed, then I would persevere. Otherwise, you may have to make alternative arrangements for one of them.