1 chook listless and not eating, 1 suddenly can't stand

Hi all! Nice to finally join, hope for some comments on potential diagnosis.
Now for the chicken sickness background.
I had chooks as a girl and me and hubby decided to have some in our garden nearly 2 years ago. So we spent one summer building a chicken tractor (moveable coop) that we discovered we could fit in our garden exactly 12 times, for rotating vege cropping. Got 6 chooks for it, young pullets, 4 bantam/silkie or bantam/Sussex (the equivalent of chicken mongrel mutts), and 2 Plymouth Rock/Sussex cross. The person we got them from said they were almost ready to lay, two might be laying already, and the others should be the right age in a few weeks except the Rocks as bigger birds might take longer. Waited and waited and WAITED and they didn't lay, till more than 12 weeks later, first month of winter, and not either of the two she said were older!

First sign of illness in coop: So about 6 months ago, one of the two Rocks got listless and not interested in eating. She would stand around with her tail drooping. Wasn't laying. If we gave them a new sort of leftover food, she would be interested and eat some (such as rice soaked in meat sauce, bacon rinds, diced banana skin, diced apple cores, chopped up left over spaghetti etc) , but she wouldn't eat anything a second day - as if she was having pain in eating and would only eat things she didn't recognise. We first thought it might be egg-bound as we thought some symptoms matched. Visits to the local vet were completely inconclusive; took an xray and wasn't egg-bound. We had her isolated and were feeding her egg and finely minced catfood and chicken mash/crumble. Vet gave a course of antibiotics, and worming. No change, eating less and less, her comb paled, even more lethargic. Her plumage was healthy and glossy the whole time. Second vet consulted, didn't have much idea, we were told it might be cancer. Eventually she stopped eating at all and we decided to put her down.
This summer we bought a taller coop (can go in) and built a fenced over yard (chickenwire enclosure) for them. We got 2 more chickens, two big red hyline/orpington cross pullets.

Sick chicken, same symptoms, 1 week:
Now, last week, another chook (bantam/sussex) "Prima" started with the same symptoms as the Rock. Prima and the first batch are now 2 years old. Listless, standing a bit stiffly in a corner with eyes closed, tail drooping. Her comb fell over! Hasn't been eating as much (weight 1.7 kg at vet visit, starting to feel underweight). The vet said he was impressed with how good her plumage looked cause he usually gets to see ratty looking hens. Didn't feel any problems and he said she was 'quite easy to feel and massage'. Prima was behaving IMHO far too docile and seemed happy to sit quietly and get head scratching behind the comb (my chooks are not tame, a couple will eat from hand if I don't move, but not this one). Runny droppings and not many (this is from one night when we looked and she was sitting on the nest at night instead of on the roost with the others, in the morning that nest had dribbly white-topped poo in) (Another hen on the other nest that night but she is broody). We discovered at vet that she has lice, but vet didn't know what the problem might be - gave antibiotics. Finished course 2 days ago. No eggs that we can tell.
She got a little bit better (a little more active, but not much) and hasn't gotten worse, but not better, and again not interested in normal food. Think she is getting lighter. When looking at how to treat the lice discovered a picture of scaly leg mites - and 2 in the coop probably have this, worse luck. Just thought it was a breed thing as the two Rocks had scabby layered looking feet not any bantams, think one of the Reds has it too. Got a special oily spray for it at the stock feed shop, will have to go out at night to put it on.
Any thoughts on these symptoms of Prima or comments on things to check for would be appreciated.

Second problem... Just today!
Just this morning when feeding hubby discovered one of the Bantam/silkie crosses named "Moppy" for her pullet afro (which receded as her comb grew) sitting on the ground and not moving to get to the food. He thought she might be trying to lay an egg on the ground. Not looking too happy. When hubby and I went in the coop with scraps to check on her and Prima, Moppy flopped around on the ground not able to walk properly. Cue panic, especially when she flopped into and sat down in the box of vegetable oil I'd put in for them to walk in to help suffocate the scaly leg mites (something I saw on this site). She got totally soaked in oil. Took her to the emergency vet since she suddenly couldn't walk - vet was not happy at having to bath her and said it was a stupid idea to put oil down like that. Her poo is just a little wetter than normal, but a vaguely unusual orangish brown, though the vet either didn't notice or didn't seem at all perturbed at the colour. The vet said she couldn't feel any broken bones or problems with the legs and she might just not be using them from weakness; left leg weaker than other, can sit upright but was listing a bit. Vet gave her a force-fed tube down the throat mixture of some nutritious glop. The vet was in a bit of a hurry because of having to take the time to bath the chicken twice; instructed me to keep her inside, in a box, sitting on towels, and with a towel as a donut so she's not resting on her keel as hard to breathe. Said to bring her back on Tuesday (3 days) for an xray to check for leg fractures, and mentioned that if it was Marek's there would be no hope.
So Moppy's here in a cardboard box sitting still as slumped down in the towel, a bit damp, when I put my hand in under her I could feel her shivering, so I turned the fan heater up a bit. Hasn't made any sound, hasn't showed any interest in the jellymeat and slivered kiwifruit I put in there for her.
Any thoughts or comments on Moppy's situation would also be appreciated. Any suggestions on what it might be? How likely is it for a 2yr old to get Mareks all of a sudden? What about the rest of the chickens? Does what Prima and our previous Rock had sound like Mareks of a different form?

Fingers crossed for both our sick girls.

Have you deloused the flock and cleaned the house from top to bottom? And then again 10 days later? Pests in large numbers will kill birds.

Thanks for the response!

Only learned about the lice very recently. we have dusted chooks with DE being careful to keep it away from their faces, installed a better dust bath for them, and have been researching external parasites treatments - a friend who is going to be a vet just told me about Eprinex which I will get.
The coop has a droppings tray full of sand which gets cleaned out every day, and I replaced nesting straw and dusted the nesting boxes with DE, so that should be alright?
It hasn't been 10 days yet.

Moppy has also been bathed (Twice) gently with slightly soapy water (after being accidentally covered in vegetable oil due to flopping into a dish of some), which I would expect to hamper any lice. She's quarantined, in a cardboard box inside.

A couple of them have scaly leg mites; our local feed store had a specific product formulated for that (which seems to be a vegetable oil base with tea-tree oil in, and maybe more, haven't got it on me to look at the ingredients) which we've applied (twice) to the legs of all seven. The one that is worst off will get more applications till we are certain it is gone and her leg scales return to normal (they do return to normal appearance, don't they??)

You need to use an insecticide to kill lice. There are several available, in different formulations. Some choose to use powders, some topicals, some bathing products. I personally use Eprinex, and have had good luck with it. I used to use Sevin, but I have waterfowl housed with my birds now and Sevin is deadly to waterfowl. DE is ineffective. If soapy water was effective in removing lice then there wouldn't be a thriving market for RID in humans.

You need to treat the birds with the insecticide of your choice and then clean out the house from top to bottom and treat that. Then you need to do it all again in 10 days. Lice and mites can be deadly to birds and would certainly explain a lot of what you are seeing. They are nothing to be trifled with.

Be wary of using anything that contains tea tree oil on birds and rodents because it is deadly if even the most minute quantities are ingested.

The leg scales should eventually return to a normal appearance after cleaning up the scaly leg mites, but it takes time.

UPDATE: This morning discovered that Moppy is now pooping almost exclusively worms. Yurcgh. Maybe she decided in her little chooky way to fast in the hopes of purging them.

However that sounds very good in terms of it may be her only problem which should be easily fixed and not as ongoing-life-debilitating as something like Mareks!

Worming them now, stuffed a syringe down Moppy's gob with some diluted Aviverm and some in the water for her and for all the other girls. Has anyone had experience with this brand before?
We wormed them (with Aviverm at the dosage on the bottle, 1 ml per 9 kg of chicken) when we introduced the two new chooks about 6 months ago, could it be she just didn't drink any of the solution at the time or can about 100 grams of worms 5-10 cm long grow in that time?