i have a cousin who has chickens he has over 30 hens that stay in a building all the time. he doesn't buy feed but goes to the bread store and buys their discarded bread. all the eat is bread and has never dewormed the birds, has lost so many. they are sickly he has offered them to me and as much as i want to help the hens i can't risk them infecting my current flock of healthy birds. i have tried to educate him to no avail. animal control states as long as he gives them food water and shelter nothing they can do. no i didn't call them someone else did. it is very sad.
Tell him that you'll take his chickens. Make them yours. Explain to him about quarantine and ask if you can continue to keep the birds at his place for a couple more weeks. During that time, insist on taking over 100% of their care. De worm them. Get them some real food. Vitamins in the water. Really try to perk them up.
After you do that, he will either see that the type of care does make a difference and learn to do right, or he'll give you all his chickens that are now healthy.
Of course you would still have to worry about long term effects and whether or not you'd want to put them with your flock at all. But it would give his girls a fighting chance.