By chocolate and white do you mean the one in the first photo? That would make me so happy. LOLI'd
I'd say your white one is likely female based on head size, but that's not my best way to sex. Pretty sure your chocolate with blue-green wingtips is female, too, because of the silhouette of the body from the side. How old are they? Between 3 and 4 months it will be SUPER easy to tell, as the males will be almost double the females' size by around 4 months (at least that has been my experience).
The easiest way for me to sex is by looking at them in profile and unfortunately none of your pictures showed that very well, except for that one duck. Females have a nice rounded underbelly and males are more flat.
Ok, I will try to get shots of them from different directions and what not. Every time I take my camera out they are sleeping. I just hosed out their pen so it is a muddy mess (and they love it lol) but I'll go take some different shots.