Thought these were blacks but wing feathers are white. Are they mottled or Gray? Think they all are short legged but not sure how long are their legs at 3-5 days.
Are they hatchery or breeder stock? That will help you with the colors.
I don’t know much about their leg length, but I know it is pretty hard to tell gender in bantams at this age, so if you really want to know, go by their personalities. Boys are very adventurous and brave, while females are more reserved. But this not a certain way to tell at all.
Too young to tell gender; post new photos when they're 6-8 weeks old. As for leg length, I'm not a Japanese bantam breeder, so I don't have any experience picking out the chicks with short or long leg lengths at this age. I think at least one is short-legged, though.