see,
because you say "node 1, node 2 and node 3" I guess they are inside the same pve cluster?
if yes, then pve cluster shares same storages (even those for backups) between all its nodes.
so if you create a storage, you create that at cluster ("datacenter") level, and all nodes see it.
if it is a "local" storage, each node has locally that storage enabled (path must exist), but this is not a shared storage so it is usable only from each nodes, really.
if you choose a shared storage enabled for backups (say, NFS), that is seen and usable from all nodes.
if your vm has a NFS server, you can mount an exported NFS share from that vm and mount from "datacenter" a NFS storage enabled for backups, usable from all nodes.
but this, as said, is a very, very bad idea, imho. don't do it.
Marco