Something we learned in 4-H is to check the feathers on the back between the wings, not the neck hackle. Rounded tips = pullet (F) and pointed = cockerel (M). This works for all except silkies, frizzles, & hen-feathered breeds such as Sebrights.

It's easier to catch them after dark with a small flashlight & just pluck them off the roost. The mother hen wouldn't do much if you pull them away & examine under a flashlight before returning.

Also, at 2 months for your type of birds as pictured on your blog the pullets would still have yellowish combs, small, and barely wattles. Cockerels will be pinked up with larger comb & wattles. They also behave differently when approached from above as the pullets squat & cockerels don't. Kids used to just wave a feed pan overhead and try to sort them out, but the feathers always confirmed gender no matter what they appeared to behave like with each other.

Hope that helps,
Corrine