It is not easy. Most breeder here have been through this stage and each comes up with his/her own way. I used to take one whole morning separate them into each container, with my son helping me catching any mantis that's trying to escape. BUt usually, my dogs end up getting some of the escapees in the mouth and foot and my wife shouting at me finding some on the ceiling. So i have decided to just transfer the "hatchery" into a big net cage and wait for the weak nymphs to die out by not feeding them for 1-2 days (Obviously this is done on species that produced tons of nymphs). However, i found out one method which make separating the nymphs easy, that is to put the "hatchery" in the fridge for 1-2 minutes at 40F, and all the nymphs then let you pick up without running around. However, i have only tried that once on S. Lineola. But it makes separating so much easier.