Welsh Harlequins: hens or..?

[Silentsun]

Hello everyone, first time duck owner here. Long story short, I bought a house that came with a pond and a Welsh Harlequin duck. She started laying eggs in May, and has only missed 2 days since. So, I decided to order a few more hens of the same breed from a hatchery. They promise 90% accuracy in sexing ducks, so I was perfectly sure all the 3 ducklings were girls. However, here we are: they are almost 6 weeks old, and only one is quacking (the one in the middle). I have a strong suspicion the one with a yellow beak might be a drake based on the back feathers. The one with a black beak looks like a hen, but she hasn’t quacked yet. Any ideas?

 

[Clucky_chicken]

Not sure about sexing based of feather coloring, but males will sound raspy look at some videos on youtube about the differences in voices. Its pretty easy to tell when you hear the voice difference a low raspy quack is a male, higher pitched happy quack female