#1- the most damaged, i believe is not saveable
#2 & 3 - Can probably be saved, i am not a soil grower, but i will give my thoughts. Go to the hydro shop, get some high quality soil (or soil less), tell them what your issue is (it is just a seedling, not a MJ seedling! They shouldn't ask if you don't offer, if they do its always tomatoes) they should have an idea of a good quality soil without nutrients. Get a bag of this, take home and take your plants out of the planters (cups) they are in, remove as much soil as you can without removing too many roots, some will come of, but most should be alright, don't be too rough. I have seen people use an air pump in water to bubble the remaining soil off of the roots. Get as much as you can, rinse them of as much as needed. Now replant in the inert soil, with either no nutrients or nutrients for seedlings (Dutch Master APS etc), hope for the best.
That is my opinion, and at least i will send you to the top of the list for a bit maybe get some soil growers in here to give their thoughts.