Its too young to tell for sure on the young black Silkies. Neither one look particularly roosterish, though. But, the larger one may be a rooster-- male Silkies are larger than the females. As for your white Silkie, I think that she's a female.
Your white silkie looks alot like my roo. Though i cant see the comb very well on my phone. the little black ones are veryyy cute, I have a little black one the same age at the moment ! unfortunately silkies are pretty hard to sex at that age. Though i agree with the previous post, usually the males are larger then the females. It'll be easier to tell in a month or so I can usually get a good guess at the genders of mine around then. good luck!