Human B vitamin complex (B50 or B100 pill - pop it in their beak and they'll swallow) is the treatment for curled toe paralysis, basically the only thing you listed you might could do something about. In bad cases it can take 1-3 months of daily pills to make a difference in the chicken's symptoms. This boy sounds bad. He may have multiple things going on. I'd also be giving him some Nutridrench (molasses water and vitamins) to help stimulate his appetite and the vitamins can't hurt.
I would worm as soon as possible, see if you can get a dog/cat vet to do a fecal float and identify worms or other things they might have. Giardia? Coccidiosis? There's stuff other than worms that can lay them low. I'd treat for all of it if you can't get a fecal float, but knowing what you're treating is best of course.
Note: if you treat for coccidiosis, stop all B vitamins - it prevents the CORID from working properly to kill the coccidiosis. You can give B vitamins again once the course of CORID is over.
There is a member on here, now a couple members, who have successfully treated Merek's with Chinese skullcap mushrooms (I think that's the name of the mushroom). My understanding is that from their observations it doesn't heal it, but puts the Merek's disease in remission (symptom free) as long as the bird takes a therapeutic dose. You'll need to keep a closed flock from then on - no birds ever go out, and you may need to treat everyone once they've all been exposed. Not a vet approved treatment in the US, but there is some literature out there about it. Something to look into.