First completely isolate the new birds for at least 2 weeks, so you can monitor for signs of disease.
Young growing birds should not eat a layer ration. You could switch to a grower/finisher or all-flock diet, make sure you offer oyster shell on the side.
So would you suggest keeping them separate for the full 18 weeks? I got them when they had just hatched so keeping them separate for virus and disease issues is already taken care of. Will the other laying hens be ok on a grower/finisher diet until we can put the little ones on layer feed? Will the older hens still give us eggs? We have an outdoor pen for the little ones, when should I start providing oyster shell and grit for the babies? They don't seem to be scratching yet.