Bare skin and poor feather growth

[lisalovli]

Hello all!
I recently inherited two Rhode Island Red hens (about 2 or 3 years old) as my Pop passed away a month ago.
Any chickens that my Pop kept always ended up losing most of their feathers - poor things!! No one is sure why and being a silly old man he didn't seem to think much of it.
I am now determined to get these girls healthy and they are settling in well.
I have powered them for fleas/mites and their diet is much improved with me. Saying that, I expected them to get healthier quicker.
Pics attached to show the one that's in worse condition. Their bums and stomachs are still very red and bare, feathers are on the back but they seem broken and no new ones coming through. They haven't changed over the last month at all. Could they have a condition I am not aware of? What can I do to improve and encourage feather growth?
Is there a mite or disease that causes poor feather growth or do I just need more patient? Given all his chickens always suffered this was it something in his soil??
The rest of my flock is fat and covered in feathers and they seem to recover from feather loss so much quicker than these girls are (one of my Sussex was recently de-feathered by the dog and she's covered in long, dense new feather growth only a few weeks after the attack, for example).
They lay really well and their eggs are huge.
Ignore the feathers on the grass - I was trimming the wings of my flock.
Thank you so much in advance!

 

[Wyorp Rock]

Feather loss and condition looks to be mainly from picking/plucking.
Did he have any roosters at all? The back of the head feather loss can be from picking or mating. Sometimes even without a rooster another hen may mount a hen out of dominance. Observe behaviors/interactions with one another especially at roosting time.

Damaged and broken feathers are generally replaced when a bird molts. Depending on their age, they may not have molted yet or they may not molt for a good while longer - maybe even next year.

You've dusted for mites/lice and see none. I would continue to check, but if they are eating/drinking/laying eggs and active, then I would just observe them.
The damage may not look all that pretty but there's not a lot you can do.

 

[lisalovli]

Thank you so much for your reply! He didn't have a rooster and they seem to get along well. He only had two and his coop was quite large. With me they have even more room as they are free range.
The feather loss/ damage is mostly on the back (the half closest to the tail) and the raw red skin is mostly at the vent and on the stomach. They look so poor compared to my Rhode Island that I already had.
I was thinking it may have been a combination of boredom (pecking each other or preening too much) and a lack of good nutrition.
They really do seem ok, just look mangey, so I will wait to see how we go.
Thank you again.