the chances of keeping two and only two female bettas in a tank together (safely with no fighting) are very small. You need seperate them now (tupperware, bowl, glass jar, whatever works) or there is a very good possiblity that you will loose one of them in the near future. If your tank is large enough add a 3rd female, else find a 2nd tank to keep the 2nd female in. Female bettas are only marginally less aggressive than the males, they still fight, nip, and even kill their competitors. With at least 3 females the aggression is spread out enough that USUALLY all the fish survive comfortably. Note: this is not a guarentee of calm living, just what it takes to make it more likely.