If you said to me "pick two fish to make a pair", I'd probably pick #4 (male) & #5 (female). I quite sure you have both sexes, but they are not that obvious - fish are still quite young.
#1 is hard to tell due to the way it's got it's body bent.
#2 is impossible to tell due to it's angle.
#3 is possibly female.
#4 male
#5 female
#6 looks smaller - possibly female, but could just be a runt male.
My suggestion is some good clean water, plenty of good food and patience.
You should set them up in a typical Hypancistrus breeding tank and wait, and wait until one day they spawn. You have both sexes but exactly how many of each sex isn't readily apparent yet. By the time they spawn, you will know how many females you have. Then remove any excess males from the group. 1 Male per 2-3 females works well.