Multiple nodes with the same peer ID is a big no no and doesn’t work.
However you can have alternative keys to use for IPNS (see ipfs key --help), if you have duplicates of that, it does likely not much. One of the peer counter will be higher than the other and only that peer publishes will go through. (that a guess, I havn’t actually tested maybe I’m wrong).
However, you don’t need to have IPNS running on all nodes for them to share the files.
You can have a single node publishing IPNS and other ones just storing the same CIDs behind the IPNS record. (there is still a single point of failure for the IPNS publishing but all nodes will serve the files).