Eh- I'd wait out the voice change. I'd say you've got another 2 weeks before you can really try to judge them. The one proto quacking you can pretty safely call a girl. The other two could be late bloomers - but after 6 weeks or so if no proto quack no girl.
For boy watch for a black line appearing around the bill and later The upper tail & coverts being lacey instead of striped. You'll see those things happen long before the curly tail feather.
For boy watch for a black line appearing around the bill and later The upper tail & coverts being lacey instead of striped. You'll see those things happen long before the curly tail feather.