I've only been reading about chickens for some years, so I don't usually give advise or opinions, but I'm just going to venture a guess.
I'm guessing that maybe these are Delaware youngsters? Based on all of the pics, the last one looks like it could be a roo, in comparison to the others which I would guess to all be pullets.
But from what I've read, Delaware can take longer to fully feather out, which helps identifying sex at that age.