Can a PersistentVolumeClaim bind to multiple PersistentVolumes?
A PersistentVolumeClaim reserves a specific instance of storage that satisfies its request. Using that same PersistentVolumeClaim in multiple Pods will attempt to use the same bound PersistentVolume in each of the Pods, which will not be possible in the case of a gcePersistentDisk.
Try creating a separate PersistentVolumClaim for each Pod.
The Lifecycle section of the Persistent Volumes doc provides a nice overview.