Ok, update, I checked last night for mites/lice after they had gone to bed and I didn't see anything moving. Is it possible that the feather loss around the tail feathers is just from picking? It doesn't seem to be affecting everyone, just about half the population?
And I got the "pasty one" as I have started to refer to him/her as bathed, I didn't see anything that looked like eggs around the vent, just the white goop that was pasted on. Some of it came off, some of it didn't but it looks like the emerging feathers should be able to come in now. (i hope)
I tried to remove the gunk but she/he started getting agitated being in the water so I had to stop satisfied with having removed most of it. I also noticed when I went to take pictures after that even though I had cleaned the vent, that there was new white stuff oozing out of the venthole, perhaps this was the stuff that was causing the pasty butt to begin with? He had used the bathroom in the cat carrier I am using to house him in for now.