Frist grow BB from fastbuds

For nutrients, in coco for seedlings, feed 0.5EC (250 PPM). Now the issue is plain over watering, which happened because the pot is too big for seedlings. As a rule of thumb, only water around the seedling, for that small plant 200 cc (half a party cup) of water is enough for 4 to 5 days

First, let me say that I much prefer shorter plants with tight internodal space. Second, your plants although they are the same age, seems like they are at different stages of development. The tallest one is on the stretch phase, the shortest one is not; once it does you should a growth spurt.