Hey there - as you know, I've been following your situation. I just checked the pictures, and oh goodness....THAT does NOT look good at all. I'm somewhat surprised they are continuing to lay to be honest; they look like they are surely in pain.
The link below is where dlhunicorn, one of BYC most respected members that we go to for medical help, keeps her medical information. You might find something helpful there.
http://dlhunicorn.conforums.com/index.cgi?board=diseasecasestudies
In the meantime, the leghorns to me look as if they are getting pecked. They really need to be separated - not only from the rest of your flock, but from each other, so you can rule that out. Do you have a way that you can do this? I've mentioned it before and you've not responded in that regard. Even if you can make up some temporary way to separate them, it would be VERY helpful. They also need to be bathed and cleaned up. You can do this by running a sink or large pail full with WARM water. I would add epsom salts. You will need to let them soak for at least 10-15 minutes to loosed the gunk, then carefully try to get as much of the dried on stuff off their bums and feathers. It may take more than one treatment. I really think you need to first rule out that they are getting pecked on first. Also, when you separate them, you can watch their droppings to see if they are abnormal, and collect a fresh sample to take in for a faecal float. Any vet can do this, and it's not expensive. The longer they stay dirty as they are, the more opportunity for infection to set in.
I don't mean to sound judgmental, and I hope you don't take offense by this comment, but if you're unwilling or unable to take these steps to try and care for them, it might be the most humane thing to dispatch them. I know not everyone is equipped or able to handle these types of things, and I for one would rather see a sick chicken humanley put down rather than continue to suffer. Also, this will hopefully stop the problem from spreading.
I DO, of course, wish you the VERY best of luck, and I wish I knew what was ailing your girls! Cleaning them up first and getting a faecal done on one of the leghorns will give you a good start to figuring out the problem. And, do check dlhunicorn's pages - there's TONS and TONS of information there. Please keep us posted!! Here's hoping you can get this figured out for your poor girls!