Can you tell by their quacks? Usually, the quack will tell the gender much faster than the drake feathers... Also, if the males are mounting, you should be able to see their "you know what" in the water. It's really long and curly, like a corkscrew.
If you find that you have 3 and 3, you will definitely have to get rid of 2 of your males, as I see you are trying to do... If you can't find homes for them, you will have to separate them. However, wait until you know for sure... I have a female Rouen who is a little confused and tries to jump on my Pekin girl when the drake is mating her. She's just strange like that sometimes and it is normal for them to kind of act out a bit, so it doesn't necessarily mean it's 2 males yet...