Those do look to be bitten off........the 2 with no broken feathers are probably the ones doing the feather biting.
They won't grow back until they go thru a molt.
The increased protein can help, but you still have a crowding situation....and feather eating can become a social habit..
Looking for mites/lice is not fun at all, especially with such a tiny coop.
Easiest if you have someone to help, they hold the bird, you part the feathers.
I do it alone at night with a headlamp, but I have a large walkin coop,
can grab the bird off the roost and sit down in a chair with bird on...
Yep, hen.
What exactly are you feeding?
Look at protein levels in your feed, label sewn onto bottom of every bag.
Also, part feathers down to skin to look for parasites, around vent, head/neck and under wings.....
....do this well after dark as some mites live in coop and only come out after...