I didn’t read the whole thread but I think these chicks had problems starting their life the first days after hatching. It could be water, feed or cold. That I don’t know.Your birds pictured are none of the breeds you listed in text.
I see 2 silver laced wyandottes, 1 red sex link and one Easter egger.
Did the hatchery send these directly to you or did you pick them up in the store?
You are at or over the recommended date from milling before the feed degrades. I recommend getting a new bag of a different brand that is 20% protein. I do not recommend Dumor, to many posts indicating poor quality.
I have experienced something similar 6 years ago with one chick. And it took a long time to figure out what was the reason for her slow growth. Not having a good start was the most obvious reason (conclusion with help of others). There where 2 more chicks of another breed I picked up the same day that did well.
Therefore I don’t think a starter with less proteïne is the reason.
At Wageningen university they did research on chicks not being able to eat and drink after hatching. If they don’t get feed and water after 36 hours, health is starting to decrease (factory farming ). If someone is interested I can ad a link to this article/research.