Currently Infuse very cleverly syncs manual library modifications across devices via iCloud. It’s not uncommon to have to fix matches because of poorly named files, so this is a huge boon. Unfortunately this benefit/time-saving only applies to devices logged in with the same iCloud account. e.g. my iPad and an Apple TV share changes, but my mother’s iPad does not.
I would propose that for whatever iCloud record is being used to sync these changes, Infuse use the native CK/Add-People functionality to allow other iCloud user’s to be added to it. Then a setting somewhere in the app for the current user to select which library they would like to use, their own, or a shared one they have access to.
P.S. Please add fully library metadata syncing across iCloud too ?