Try this little trick, it's not cruel in any way...
Pick up the chicks by the legs and let it hang. If the chick curls up and tries bite you or just peck away, then it is a hen. If the chick just hangs there, no curling, then it is a boy.
If that's too hard to tell, then pick them up by gently pinching the back of their necks, if the legs go up and curl, it's a girl. If the legs dangle, it's a boy.
I'm not sure if your chicks are too old for this trick, but still worth a try
If still unsure, then try wing sexing.
Spread out their wings, if the feathers are like this- IiIiIiIiI (Ignore the dots above the "i")
Then it's definitely a girl.
If the wing feathers are like- IIIIIIIII
Then it's definitely a boy.
If STILL unsure, then post pics of their wings and reactions to the pick up test. I'm sure people will be able to identify their sex.
I hope I helped, let me know what you find....