Is there a reason that you MUST know the sex right NOW? They are very young to be trying to sex them definitively. I know you said that you are almost certain that #1 is a cockerel and it is the only one that I would have guessed might be a pullet, it and maybe #3; but I'd just as leave flip a coin really. They just don't have enough comb yet to make a reasonable guess.
Sorry I couldn't do any better for you. Give 'em another couple of weeks or so.
I'm trying to figure it out because chick #2 is trying to crow. I'm not allowed to have roosters and would like to try to place them all together. I was still hopeful about 1 & 3. Once he starts to get too loud he has to go before a neighbor hears him.