You need to cut out or cut back on the scratch. scratch is not feed, it's the chicken equivalent of say, fries, not a lot of nutrients but lots of carbs and fat. Your chicken's are likely suffering from nutrition deficiency.
You don't mix it with their feed, you throw a handful on the ground for...
They are fine to sleep outside, this issues is not caused by getting fresh air.
The feathers could be genetic or depluming mites, the poop but is from a crop issue or worms.
What's their diet?