Set up the backups:
Connect your NAS to your master VM. All other VM’s will connect to the master to backup there. Your VM’s will need to connect to your private network so each VM will need two NIC’s.
The SAN is attached to the hypervisor (ESXi) and then you can add a virtual disk to the machine that is going to act as the backup server.
IE, create a datastore to be able to then allocate the diskspace to the backup server VM: