None of the chicks are showing comb development typical of a cockerel, but that is not unusual for 6 week olds. Feathers on the saddles just before the tails are rounded for pullets and slightly pointed for cockerels. Also a cockerel will have bigger feet than a pullet and will have an obvious button for a spur on the legs. Some pullets will also have that button so don't let that be a determining factor. May have to give them a few more weeks...#4 may be a sleeper cockerel....if there is one.