Its good you separated them - as the alpha will always pick on the other one. In a group, they will establish a pack order - like wolves with one being the alpha female and the others being the subordinate bettas. The more there are, the less likely the same one will get picked on. Of course there is no guarantee they will get along anyways. There is always the chance you will wake up to a badly injured or dead female.
I like my female tank. If you can, I would get a 10 gallon and get 2 or 3 more females but make sure you do some research before you try this.
And make sure the tank is jam packed with plants and decor. The less they see each other, the less they will fight.
Also, make sure you have a spare tank incase one girl is too aggressive.