I think there all pullets but the black maybe a cockerel because she (probably) has a little bit bigger comb the the other 2 pullets but I think she if a pullet because their would be a way bigger comb if it was a cockerel.
The 3 are females, if they were makes they would have a way bigger comb and at least a little red on the comb at 12 weeks, first 2 picture is my 15 week old cockerel (male) and the 2 last picture is my 15 week old pullet (female), you should be able to tell the difference at 12 weeks between a...
I think it is a female, because I have a 15 week old female and male silkies and if yours was a male she would have had a bigger comb by now. The first 3 pictures are my female (Katrina) and the 2 last one or my male (Ian).