looks like some serious PMS going on there
(Plant Moisture Stress)
hard to figure whats wrong with plant 3,4 other then moisture stress from the flush..
i too would recommend starting from scratch with a sterile everything.
from what a have seen those plants are gonna have a tough time flowering.
it seems like your on the right track with nutes, light, neem.
i think i would off plants 3,4 and focus on helping the decent looking plants.
do you have any experience with cloning? i would use plants 1,2 as mothers, clone them and veg, then bloom clones.
good luck