TOTW High Prairie Puppy is lower in calcium and safe levels for GSD ( have a 5lb bag to try). It's grain free but not lamb. Since you want to use one food for all your dogs, maybe Orijen. Most of their foods are lower calcium. Their 6 fish has lower calcium levels (1.4-1.7%).
Earthborn Holistic Meadow (it's lamb) is low calcium. I haven't tried it. My pup has food allergies so I have been doing a "LOT" of dog food research lately. Just my input....Best of luck to you!