I don't know how you are set up but you may have a few more options.
1. Can you let them all onto your pasture? If they can they should all return to the coop to sleep at night and if they are used to laying in the coop they should return to the coop to lay. That's the way Dad managed his.
2. What is your general feed? Usually the only difference in feeds is percent protein and percent calcium. Layer has about 4% calcium, all the others have about 1% calcium. Protein for either can vary. The higher percent calcium in Layer is for egg shells, the ones not laying don't need it. Depending in what that "general" feed is you might be able to give that to all of them and offer oyster shell on the side. I don't know where you are located or what your feed options are but that might be an acceptable option. Oyster shell is usually pretty inexpensive, the ones that need it for egg shells usually eat enough and the others don't eat much. That's the way I feed mine.
To me the best way to determine if a hen or pullet is laying is to look at the vent. If it is soft, large, and moist-looking they are laying or are about to. If the vent is tight and dry, they are not. It does not tell you how often they are laying just whether they are or not. When you see both moist and dry the difference is pretty obvious.
