The birds really need to be on commercial laying food. Corn does not have much nutritional benefit for a chicken. They love the cracked stuff sold as scratch, but it is meant for a treat only. The birds are skinny and sick because they are essentially starving to death. Can you get some chicken food for them soon? I would also de-worm them, because the chances they have worms is very high. You can buy wazine from the farm store and mix it in the water, or a much better medication is valbazen and it is ordered from Jeffers online. I wouldn't wait for that to come, they need help ASAP. I would also give them a dusting with Poultry dust or sevin dust also from the farm store. This will kill lice and mites which may also making the hens thin and sick. So,
1. Chicken food for layers-get as soon as you can
2. Worm them-worms will take nutricion from them
3. Dust for external parasites- MUST repeat in 7-10 days to get newly hatching bugs
4. Plenty of clean fresh water available at all times
I hope this helps. Read all you can on here, there is awesome advice on raising healthy chickens, Good luck!