Female crown tails are the easiest to distinguish, they have itty bitty little "spikes" that stick out on their fins. If you got them from a pet store, and they don't have the obvious spikes, then they are probably veiltails =)
My Current bettas:
Sullivan- Orange rose tail halfmoon male
Daisy- Mustard Gas (black and yellow) veil tail female
Milton- Teal butterfly halfmoon male (mom's betta)
DFTBA to nerdfighters working to decrease world suck!