Back when my wife was breeding Betta splendens, we kept females of average temperament together, 5-6 fish per 10gal.
Caution, we learned that <5 or >6, was a recipe for territorial aggression, less and they seemed to have time to concentrate on one or two weaker fish in the pecking order, more and the crowding caused aggression.
Not to say that the pecking order didn't get rough sometimes, but they weren't tearing each other to shreds/killing each other, nipped fins were the norm.
Also, some females are just as territorial aggressive as the males, and will not share a tank, thankfully most will get along reasonably.
We loved our Bettas, but the birth of our second child left no time for my wife to maintain the breeding hobby, taking care of so many tasks, males, females, breeding, fry, live fry foods and daily maintenance/PWCs.