all but one of my female bettas live in a 29 gallon, 6 or 7 female bettas with 1 molly, 1 platy, 5 gold tetras and assorted small corys. the tetras play with the tetras, the bettas play with the bettas. the tetras and bettas 100% ignore each other.
the only thing the female bettas have ever done is throughly check out the corys. they were not aggresive at all, just eyeballed them a lot. I think they expected them to be very ugly bettas.