Definitely one girl in there, the first one in the coop. You can also hear some raspy peeping which would be the boys. I still think you have one girl and three boys.
You have beautiful ducks! I know they look like girls but they all start out with coloring like a female (juvenile plumage). If I had to guess, I think you have 3 boys and 1 girl. The girl is in the upper left of the pictures. As others have stated, you can voice sex. There are additional...