Hard to say for certain with only that view, but seeing the size difference, I'm guessing the white one is male, and the buff's a female. Or, are they the same age?
I have 3 white silkies 1 is definitely a male he is smaller than my female, few pictures of him, not the best quality but I think you can see the black comb on him the females only have furry where his black comb is. There still young but I do believe this is my only Cockerel
Lady I got my Silkie from made sexing Silkie a bit easier for me. Cockerel/Rooster have longer feathers on their heads that stick out, plus redder and larger combs and wattles. Also they get more wing feathers and aren't as fluffy as the Pullets.
The white silkie is definitely a cockerel, the non-silkie bantam is definitely a pullet. The leaves the darker silkie, which is probably a pullet, but it is not 100% just yet.