I agree, they're probably not laying due to the short days. When they days get longer, they will start laying.
Another option is to continue feeding the grower for the rest of their lives and keep crushed oyster shell on the side. They will eat the oyster shell when they need it and won't when they don't. This is easier because when one of your hens go into molt (in another 6-12 months), she will stop laying and shouldn't have layer feed during the molt. You would need a seperate coop to feed her and it would be stressful on her to be seperated. If all 3 of your hens molt at the same time, it's a moot point, but that probably won't happen. Even if this did happen, while you wouldn't have the issue of splitting your hens up during the molt, you would still need to buy and feed grower or starter feed during the molt.
The only difference between layer and grower feeds is the layer has a lot more calcium and the grower is usually a bit higher in protein. The extra protein is good for them.
Feeding layer feed to a non-laying adult chicken can lead to visceral gout and kidney problems. Feeding it to chicks can result in deformities or even death.