This one still has part of the membrane attached to the cotyledon. It wants to open, but the membrane is still holding it. Give an eyedrop of water where that membrane is still hanging onto it, to help it along. Give it some time. Try not to touch the sprout, it's pretty delicate right now.Finally, Lucky. He is still bending over, almost in a U. (He is not touching the dirt on both ends of the U.) I wonder why he is bent like this. Seems like it is the light source, which is maybe too far. I need to read up on this on the 420Magazine www and see.
That soil seems a little dry, but I can't say for sure. Is the bottom of that soil pretty dry?
What is your watering method and how much/often?
Seedlings need light, from your tent pictures the lights are up pretty high in there. You want them to be closer to the babies than where they are in my opinion. Be careful they aren't too hot. If you hold your hand between the light and just above the seedling and your hand gets uncomfortably warm then it's too close/hot.
Don't give up on this one, it needs to shed that membrane and it might need some more moisture. Let's see what other opinions are.