If your climate has been warm and wet lately, it's possible you're having a coccidia outbreak and your chickens are now suffering from coccidiosis, a parasite in their intestines that eats away the lining and causes blood in the poop. It can cause death. Quail and chickens have different coccidia species that target them, but the treatment is the same for both.
The cure is a vitamin B blocker called amprolium. You can buy it under the label Corid. You'll see two different dosage recommendations, one for prevention and one for intense treatment. You will need to do the second one, mixing it in the chickens water each day fresh for five days. Then repeat again in one week. Don't give vitamins during treatment.