Good morning and welcome to BYC!
It would be helpful to have a little more information. What are the ages of the birds? What breeds are they? Did you go through an integration period before mixing them all together? How much room do they have in the coop/run?
If the younger birds are not laying yet, they shouldn't be eating layer feed because it's too high in calcium. If some of your birds are laying and some not, they can all eat grower feed with crushed oyster shell provided on the side.