Within the object authority you can set this authority. “WRKOBJ libraryname” From here take an option 5 to view the authority that is currently set on the person’s library. You can do a *Public Exclude or set an authorization list and if they can alter, reference, etc…
Sorry, but “object” authority <b>does not</b> allow this kind of authority maintenance. The “object” is the file, not members of the file. All members of a file belong to the same user. Different members are not owned by different users nor authorized to different users.
The question has no satisfactory answers since members are not intended for this kind of use.
Use different files for different users if authorities must also be different.