To delete the usernames you must be a Domain Admin with privileges over user account management. Then you must use the Active Directory Users and Computer tool to delete the accounts.
Usually to hide resources in a domain environment requires that you create Organizational Units or OUs within the domain, and then place the resources in that OU. You should be able to place the printers and the computer(s) in the library in a Library OU. Then only when logged into that one (or few) systems will the library printer be visible or usable to users. Here are some useful docs on this:
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