Multiple Backend Users as single Frontend User

Attach a custom user meta field to all of them – for e.g. a checkbox. Then, in your template, simply query the user meta field and if it is checked, just output the shared user name instead of the user profile field you would use for other users.

If you want to make sure that users can not attach themselves to that “group”, you will have to wrap the addition of that profile field with

if ( current_user_can( 'manage_options' ) ) { ... }

to restrict it to “top” users like those which have the administrator role assigned.