Welcome from New Orleans. The hen that is having tarry stools, is it every stool or just occasionally?We have had hens who laid eggs with spots, can you get a picture of the egg as well, are the spots on the outside of the shell or inside when you open the shell?
Happy Holidays
Tarry dark poop can be a sign of internal bleeding, you should definitely post on our Emergency forum for more help and suggestions. I hope you can get this sorted out soon!