I will need to obtain some layering food pretty soon as my chickens are about 13 weeks now. Does anyone have good recommendations? I would prefer the soy-free kind. At what week do I change over? I have 5 chickens that are 2 weeks behind in age. Do I have to feed the older chickens separately or can I mix in the layering food with the pullet food until all are 16 weeks? How does that work? Thanks for all the help here!