What medium are you using? Those plants look like the are being grown in a brick. Marijuana needs much more aeration in the soil than that to grow at optimum levels...
As far as showing sex I don't think you can tell by any of the pictures.
I suggest breaking up that top layer of...(dirt) and adding in some perlite. Be gentle and don't go to deep so you don't hurt the roots...or that's what I would do. Maybe even transplant into bigger pots with some better draining soil? As it is now, I fear those wont yield much even if the are female.