How to get quails to breed in captivity?

I have 4 domestic quails in a large chicken coop, 3 hens and a cock. They have the right environment and the right diet. I want them to start laying and hatching their eggs but they're not. I've had them for 9 months now and still nothing and we're coming to the end of spring. The hens are missing feathers at the backs of their heads, showing signs of breeding but still no signs of laying. I don't know what to do, can anybody help me?