Oh my :-( I'm so sorry! I hope everyone improves!! As far as lice, it doesn't necessarily relate to bedding. When a bird is sick, of course, they don't dust bathe and preen like they would. So it definitely gives lice/mites a chance to get out of control. Everything I've read says if your bird has large amounts of them, wonder what else is wrong with them.
I hope for the best for you and your chickens!
I hope for the best for you and your chickens!