Well, I'm not the greatest at this, but I'll take a shot at it. I usually compare my chicks to their siblings of the same breed and age and have so far done fairly good at it.
1st is a pullet
2nd has me thinking roo, but I'm not entirely sure. I've seen early bloomer pullets that looked like that
3rd Silkies are beyond me! Sorry.
4th looks roo
BUT... I personally wouldn't get rid of any of them until they crow because then you really know for sure.
Now let the real experts take over.