From what I have read, chicken lice does not transfer to humans.
A nice dust bath of fine sand, a handful of wood ash and a handful of diatomaceous earth, available at many garden stores or the garden area of some big box stores, will help with mites as well as general chicken comfort. You can place a cat litter box in their run for this, or an oil pan from the auto store works nicely.
A good diet and a run with available shade and green things to eat and scratch in will also help.
I agree with a previous post that the one who has all her feathers is probably the highest on the pecking order, and the one with the least is likely the lowest. More space and better nutrition should reduce the need to peck.
Worming them may also help. Some recommend stirring a few tablespoons of diatomaceous earth into their feed once a month or so to treat/prevent worms naturally. I do this with my birds, but I don't know how I would tell if they had worms. They all have all of their feathers though, and are happy and active, so it doesn't seem to hurt them.
There's lots of advice online about breaking a hen of being broody. I haven't encountered this yet, but I think it can be harmful if it goes on too long, as they eat and drink very little when they think they are sitting on a nest.
There's never a guarantee that any animal you take in will thrive, but does that mean you shouldn't try? Especially since you don't have other chickens to worry about bringing potential chicken sickness to. It sounds like they will have a far better chance for a happier and probably a longer life with you than where they are now. Best of luck if you do go for it!