Hard to tell yet, a few more feathers would help. If I had to guess I would say female Rouen and male Khaki. I have had a few females start voice changes at only three to four weeks. They sound like stepping on a low, croaky dog toy.
Check out this post here . The post was updated with the actual genders at the end (the original poster was right, 5 boys, 1 girl). I will still stick with checking the feathers above the tail. If you look at this picture from that post, you can see the girl has the lighter, two-toned feathers...
With Khakis you can tell by the feathers above the tail. Lighter, two-toned feathers indicate a female. Dark, one color feathers indicate a male (see picture below). In your picture, the Khaki on the left is hard for me tell. It looks like a female but it could be the lighting and shadows...