Why are the tops growing so fast? They're about a week or week and a half old. Also can the sickly looking one be cured?
what kinda soil are you useing? what is your PH and humidity. I myself cant see anything wrong besides that you popped all of them in the same container. That can be a pain man when you switch to flower. I would guess PH but Im not entirely sure myself.
The growing medium isn't deep enough and they should all be in separate containers. They're likely stretching because they don't have enough light. Other than that, you'll need to provide some more information. What's the growing medium? How's the pH? What kind of watering schedule are you on? Any nutes yet? What lighting are you using? The more info, the better.
put a fan blowing on them ...you really need to READ READ READ about growing , as you are clueless does your planter even have drain holes ?
I'm guessing (hoping) he's just got them in there for germination and wouldn't need drain holes. It's too early for a fan and those seedlings aren't strong enough. They should probably be transplanted into something appropriate, like a Solo cup with good soil.
There is a number of things done in error that I can see in that picture but first and foremost I have to ask as to whether or not those are even cannabis. While the first single leaves look correct I have NEVER seen a growth pattern like that even given poor lighting.