They are WAY to young to sex. Wait till they are 3-4 months old then you may have a more solid idea.
Girls can take up to 9 months to lay, I've heard of roosters fooling you into thinking they are hens - very henny crests, little to no wattles or comb, until they crow at 9-12 months old. lol Silkies are the hardest breed to sex. Unless they are hatchery chicks - hatchery chicks tend to be very easy to tell by 2-3 months old. Looking at these chicks its hard to tell on many of them...Give them another month before making serious guesses on most of them.
That buff is a rooster, its also got a single comb, the wattle development and that big reddening single comb are a sure fire that hes a boy.
out of those last pictures the first one you'll get a good idea on is the brown chick - the partridge. Partridge color in differently (boys/girl patterns) and its still too young to tell.