Geese are super hard to tell before they are adults. If they have the knobs on the top of their beaks like white chinese (which I believe they do) you will be able to tell when they are several months old, but sometimes behavior is the best clue. My gander is very aggressive and protective while all the females tend to stand back a little more. The gander is really loud too, much louder than the girls. How old are your geese now, and can you post some pictures?
Have you ever seen Jurassic Park? Where they have that Velociraptor whistle thing? my male goose sounds JUST like that. sort of squeaky breathy, LOUD honkwhistle sort of thing. he was born in April, and by late july his head bump was taller than his head.