Keeping female bettas together?

I have three female bettas. Each are different sizes. One is a big matured crown tail, one is medium sized spade tail, and the last is a quite small roundtail (not plakat). I have a 6.5 gallon tank with lots of plants, a flower pot and the water is treated with indian almond leaves. I have tried introducing them in neutral territory, so I added all three at once at the same time. They started fighting in a ball. None of them suffered any fin injury or horizontal black lines of distress. Nor did they try to flee. However, I got frightened and separated them again. Please give me lots of advise, have any of you tried this? Is three females enough to form hierarchy?