IMO, your plants are terribly abused, but now, it looks like you have a handle on it. If your soil has nutes in it, and I'm pretty sure it does, that's a lot of your problem. Seedlings dont need nutes. Thay have enough energy stored in the seed to last them awhile. Over ferting as well as the other probs mentioned can kill them for sure. They look nute burned, light stretched, overwatered. Check the pH and ppm of your grow medium and see where you are. Like a few folks said, READS, READ, READ, then post questions. Your next grow will be 1000% better.
Luck!!!!!!!!!!!!!!!!!!!