I see for sure two that I would bet money on are likely hens, and a most definite drake in the bunch. Give them a bit more time. I was able to call my drakes for sure at about three months. But I also use to purposely stir them up a bit to get their excited quacks in hopes of being able to notice a difference. But in all reality, I could tell very early. Even as tiny ducklings, my drake was never overly vocal, barely doing much more than peeping, while the females would just vocalize over any little thing.