WHen they start laying, you will know if they are getting enough calcium by the eggs. they will be hard or soft shelled. EIther cut back on treats or up their access to calcium like oystershells, and feed back the egg shells to the girls.
As the girls are 9 months, and you have fed them properly for their growth period, you can swtich to a layer pellet. Usually about 15-16% protein and about 3.25% calcium. When laying, their feed intake surges to be able to make those eggs.
I would buy layer pellets and mix it into the last of what you have been feeding and that way they can get used to the new grain without jumping from one to the other cold turkey. SOmetimes they don't like change.