IMO 3 fish in a 3 gallon tank is far too many for the size (for bigger fish). The damage that you see is from them nipping each others tails. Female bettas are not friendly to each other, even when they're in larger tanks. You can do a female sorority but you need more females and a much larger tank. 10 gallon is the recommended starting size, but the bigger the better. Here is a good thread to read. http://www.bettafish.com/showthread.php?t=29402
Your female bettas need to be separated and put into their own tanks ASAP. They will not get better in the 3 gallon tank you have for them when they are all together, and you will most likely have dead fish on your hands if you keep them together in there.
Once they are separated, I imagine they would begin to heal. You can do what LizzyP said, but clean water and frequent water changes would be the best for them once they are in their own tanks.