I've lost 3 hens.. I need advice/help

Hello chicken lovers,

I don't know what is happening with my flock. I lost my smallest frizzle at the beginning of Feb. She stopped roosting one night and then the following night same thing. I picked her up to put her to bed and I set her down for a moment and she almost completely collapsed on her side. I noticed she was breathing heavy. I put her to bed and she was dead in the morning.
I then noticed that one of my polish frizzle hens wasn't bearing weight on her right leg. When I inspected her I was shocked to see large open sores w/pus crusted around them. I Googled the foot/leg problems and was shocked to see scaly mites.
I was blown away bc when I went thru a breeder for frizzle hens I noticed how ugly their claws were. Being a new chicken keeper I just thought that was part of the breed. How wrong I was. I have been treating my hens w/soaking their legs in a warm soap bath, Exfoliating their claws removing layers of scaly mites. After that I rinse, spray wound wash, rinse, olive oil, topped w/a thick coating of petroleum jelly.
Tina, the hen w/open sores all over her body was kept in a seperate area then the flock but still outside where everyone cld still see one another. I also put her on an antibiotic treatment and she seemed to get much better. I took her off the antibiotic water and she reverted back and the sores came back. She fought hard for 11 wks but passed away 2wks ago.
I bleached out my coop, got rid of all the fertilizer, bedding, and droppings which I was composting since the fall for my garden.
2days ago I noticed my cochin bantam hen stopped hanging out w/the flock. She was staring off most of the day. She was still eating and drinking. I noticed she didn't roost mon night. Last night same thing. No roosting, staring at the wall. It was like my frizzle back in Feb. I picked her up and saw the same breathing patteren as my frizzle. I wrapped my cochin in a towel and held her for a while. I knew she was dying. After a while I put her to bed and said my goodbyes.
In the morning she was barely alive and when I got home from work she had passed.
I don't know what is going on. I have been working diligently trying to save my flock.
I have had my girls on DE food grade, water w/vinegar, they get fresh greens regularly, chicken scratch, crushed oyster shells, and protein pellets.
I live in the upper Northern California area close to Oregon. My coop was built during the heavy drought and seems to be fine. This year when the rain finally came the coop was wet on the ground and flooding. I put wood boards down like planks and the girls walked on them but were still in the rain when they left the coop. I have a very large coop 6ft x 8ft for 6 hens all med-small breeds with lots of space and tree limbs for roosting.
Any help, ideas, similar experiences would be greatly appreciated..