You can keep several females together in a tank BUT ONLY IF they have been acclimated to community living first. This is the safest way to go. Otherwise, if you just buy individual females and stick them together, you might be in for a nasty surprise! Although female bettas are a little less aggressive than their male counterparts, they too will fight. They will display at each other and flare and attack and pull each other's hair out LOL. You can take your chances and you may be lucky but if you do, remember to keep a very close eye on your gals as you might have to separate them, jar them, or pull a bully out.
Male should not also stay with female on the same tank unless for breeding for they may kill the female.
Male Fighters should not be kept with species that have large or flowing fins like fancy guppies or angelfish because they are sometimes confused with other male bettas.
To be safe, I always keep one betta in a single tank.
