Hello,
The black and white ones with the barred patterns have a name that suits them. They are Barred Rocks. The red ones look like production red's and the one black is an Australorp.
You have a beautiful flock of hens. Absolute no roosters. The one in second-last photo, far back, may be a rooster if I saw a better photo... But most likely hen.
The bare-backs may be cause by mounting, (but in your case- I honestly don't think so). My foggiest guess is that your BR's (Barred Rocks) are the culprits. They are spotless. No bare-backs, right? This most likely means that the Barred hens are the bullies of the situation.
You can use anything to cover it that you get advice on, from gel's to aprons... (I prefer more natural than the gels sold)... But I'd let it be and just pluck a feather from the bully when they go to peck an innocent hen.
My hens had a bully at some point in time... I let them be and they are all healed now. They are nine years old! I think they were fine.
Also... Your hens may be stressed. Give them plenty heat in the winter and perches all year round. As long as they can escape a rude hen... They can handle themselves and heal.
Your hens are fine! Just don't let the mean ones win. Good luck, God bless. I hope this information helps you on your journey. You have beautiful hens that look healthy.
Have a nice evening!
Regards,
-The Angry Hen