What is happening to my chicken's feathers?

[KRS57]

Damage is from mating and plucking.
The hen with the loss on her neck is being plucked - likely from a neighbor during roosting.

The issue didn't start until you introduced new birds - how much space do they have in Sq Ft - coop and run?
Changes within the flock can be stressful and birds often feel they need to compete for food when newbies arrive.
Make sure to provide several feed stations to spread the birds out.

Is the Scratch and Peck a loose feed - meaning it has whole grains or is it pelleted? Often if you feed a loose type feed, birds will pick out only the good things they like and leave the rest this causes for an incomplete diet - the feed as a "whole" including the powder is "complete" - fermenting or soaking feeds is one way to encourage them to eat all of it instead of just picking through it.

I don't really see anything that looks like mites/lice, but if you feel they need it, give them all a good dusting of the permethrin.

I think the issue started right before I introduced the new chicks and the issue became very noticeable and got worst after the new chicks were added. We were overcrowded when the chicks got bigger. We had 16 chickens. Added 8 chicks. We gave 4 chicks and 4 hens away. They were probably overcrowded for about 1-1.5 months.

My hen house is ~8 feet x ~8 feet. I have four nesting boxes. My run is ~30 feet by 15 feet. I have four feeders in two locations. I have two water stations.

I think my husband feeds them the whole grains, but we mix it with the Dumor chick starter which is def pelleted. I can ask him to switch to scratch and peck pelleted.