Okay yes, as everyone else has mentioned. These are Cayugas! They look almost identical to mine, I have three also. Mine are 4 months old on the 16th of this month. My male got his tail feather yesterday and it is very pronounced! I noticed that yours are in the stage of developing their "flight" wings. No they won't fly off but they will be able to get 6-7 feet off the ground. Mine developed those feathers last month, so it makes me think yours might be a little younger than 4 months, maybe ~3.5. You will start to see more colors when those feathers come in. I have also noticed that one of my ducks will sometimes have a feather that looks like a tail feather, but its not, it's kinda like a "bad feather" day. The things that I noticed about mine were; the ducks, have lighter legs and feet, whereas the drake had darker legs and feet. Also, my drake tends to stand a few inches taller. My ducks also have quite a bit of brown lacing on their chest, and the drake doesn't. I know that both of the parents of my ducks were Cayugas, so I know that the brown isn't any other breed coming in. My drake has lots of green and blues! The ducks have a good amount, but not as much, also their heads aren't as green as the drake's. As far as the differences in the voices, I tried to do that, but all mine sound the same. Honestly, I was wondering, for a while, if I had all three of the same sex. Now, I know I don't!! I had the impression that I had two ducks and one drake, and I now know that was right! I will post some pictures under this post. (So you can compare.) Good luck! You should also start finding eggs, depending on their age. They should start laying around 18-22 weeks, mine are 16 weeks.
This is my drake "Racer" If you notice his head is pretty green, more than the others. If you notice his feathers are fuller than yours are, yet.
This is his tail feather, I will post more pictures from yesterday in the yard. This was taken on Sunday afternoon. I wasn't sure if this "was" his feather or not. I took this picture in case. Later that day when I let them back out, it was flat again, so I didn't know if it was or not. Now I know, after what it has developed into. It was his tail feather!