Agreed.Sorry that the one chicken is worse and losing weight. It sounds like the chick has a prolapse or damage to the vent. Being less active and weak sound like coccidiosis. I had suggested amprollium earlier, but sulfa antibiotics can be used to treat coccidiosis if you can get some. I would give some plain yogurt to soothe the bowel. I would keep trying to get it to eat some wet mushy feed, and give electrolytes and vitamins.