It all depends on breed and living conditions. Some breeds are known for laying eggs well into their 4th or even 5th year of life, whereas others will start decreasing within their 2nd year. What breeds do you have?
Also, hens don't lay often in fall and winter due to the shortened daylight hours, colder temps and little access to the outdoors. You could add artificial light to encourage them to continue laying throughout the winter.
Stress can influence egg laying as well. Are your birds molting, injured, being bullied or have parasites? Could they be hiding their eggs at all?
Hopefully, they will start up again in the spring. Remember to provide them with plenty of food, water and calcium and know that they decrease in egg laying a little more each year of their lives.