As @meyay stated, it’s a bad idea to have two manager nodes.
Note that manager nodes can be used for worker tasks, too. Just make sure to constrain the CPU usage of the workloads to not take up 100%.
Furthermore running a database with a network file systems seems also totally not best practice. Databases are usually build for fast direct access to local files.
You probably want to ensure the underlaying file system when a node breaks and the container is moved to a different node. But for databases this is usually done with a primary/secondary setup or a DB cluster, not with a shared file system.