Maybe... with all the ducklings I've had, by the time they were fully feathered, it was obvious who was a boy and who was a girl. At that point, those that still sound like baby peeps are most likely young drakes.
You should definitely be able to voice sex them by now! My little swedish girl is SO LOUD right now and she is about the same age, maybe a bit younger. You've got some cuties for sure, I love the speckled beaks!