T, be patient on the pre-flowers... just pay close attention and you will catch the males early enough. It would be better to let them turn for sure than to yank a girl early. From the pictures I've seen, it looks like you will turn out with 2 females and 2 males. Hopefully you get one healthy female from each strain. Are you misting the plants at all? Ideally you should mist them early in the morning (before or right after lights turn on). It looks like a few of the leaves are suffering ... is this from pests, nutrition, or overwatering? As some people have said, make sure you're "cyclying" your plants and letting them dry up and crave the water before watering again. Also, the plants are most active right before the lights come on and they will take up water and nutrients more rapidly if watered early (when the lights first come on). This also goes for the leaves, if you mist them early the leaves will transpire rapidly and increase vigor. Give the plants water only when they need it and try to use aerated filtered or distilled water. If the leaves continue to suffer, consider removing the diseased leaves. Also, are you thinking about FIMming or pinching soon? I think you should top em early so they get bushy and keep a lower profile. As far as the sexing, look to the bible or search online for a picture of male and female pre-flowers, these would be easier to see with a microscope or magnifying glass. How has the temperature been? Are you transplanting again when you sex?
Be patient with the males, but don't wait too long or they might splooge! Keep on Truckin.
Peace,
CCC