Is it normal for the girls to be lower to the ground? Her chest is big and it almost touches the ground when she walks in search of bugs and tippy toe chest does not do that.
The undercarriage of the girls is generally lower but I find the whole flight feather thing pretty conclusive. I have just had 5 ducklings where at 4 weeks 1 was small (duck), 3 were large (drakes) and one was inbetween and was frustrating me. Even though she was much larger than the other duck her flight feathers came in at the same rate so I guessed duck and 3 weeks later she is obviously a duck just a large one. So I would say you have one of each Yay
I love my Muscovies they are just like dogs when they wag their tails and knock on the patio doors !