Sometimes it is not the soil but how much you water. Seedlings take a small splash around the base of the plant, never water the whole pot, just where the roots are in the pot.
Even after years of growing i still overwater now and again, roots need to breath every 4 days by rule so make it so!lol! Seriously never stop learning how to water, you think you are doing it right but it is rarely the case. Small 3 inch pots allow the small volume of soil to dry in a few days and allows the roots to breath which is why seedlings need small pots and repot up only when roots have filled the pot and even then repot a 3 inch pot to a 5 inch pot.
I feel it is the basics which get the least attention and are often overlooked, learn to grow a healthy plant from seed first then learn the veg period, dont just limp along with a problematic plant. I wish i could send you some seed, i got white widow feminised 75percent indica 25percent sativa! Dutch passions best from 4/5 years ago. Smoking the sh!t now and my head is frazzled, nothing better than your own crop, taste the hard work!lol!
Post pics now if you can and everyone can see what is going on, i feel you need to stabalise the plants first. Peace
