Volumes can only be used by a single VM at a time (they’re basically just local disks that stick around between reboots).
Syncing data between volumes is a hard problem .
For apps that need multiple VMs, most people end up writing files to S3 or similar. Then they treat the local disks as a cache. We do this for our docker registry, we use Minio as a caching gateway on each instance and point them all at the same S3 bucket.
What is your app doing with files? If you need to write to a local file system that’s “shared” across a bunch of VMs, you can look at exotic clustered filesystems like GlusterFS. That’s complex though.