Don't scatter the oyster shell around. Put it in a container that they have easy access to. Scattering it around like you would scratch makes it likely that it will be eaten by ones that do not need it.
All of my adult poultry are on a 20% protein All Flock feed whether they are chickens...
I would feed all of them an All Flock or Flock Raiser feed along with oyster shell free choice.
The turkeys will not eat the oyster shell as long as it is offered free choice and not mixed in with the feed.