this time a question with pictures

How often are you watering? What is your soil mixture? Do those sack looking containers actually allow excess water to drain off?

Looks to me like possibly overwatering and almost certainly a ph problem.

What is your soil mixture?

What are you using for nutrients?

How often are you watering?

How often are you feeding?

Should be able to narrow this one down.

Do you have a ph meter?

yes that looks like all 3 you mentioned....... i would not feed the big ones the same as the lil ones , and it looks like the lil ones need to dry out just a little before watering again. the big ones look fine they might even need a lil more water or light. what kind of dirt and what kind of light ? they all also have signs of heat stress too, but it looks like they will be fine ... mainly the lil ones just need Less food/less water.