Some breeds take a few more weeks to start laying than others. Since yours were hatched a little later in the year and coming into lay when the days are the shortest, they might not lay until a little later, when the days get longer. There's nothing about that food, that would keep them from laying. They'll lay eventually. I know it's hard, when you have people telling you it's your fault or you're doing something wrong. Really, they will lay when it's the right time for them. You aren't doing anything wrong.
I just thought of something. Did you mean you have been feeding them this food since they were chicks? If so, then that would delay their growth. Layer feed has less protein than chick starter. They would take longer to mature, because they wouldn't have enough protein to build their bodies with. If you had them on chick starter until recently and then switched to layer feed, then it's no problem.
