If SharePoint out-of-the-box approach to editing properties (metadata) for multiple documents is impossible, then for you and your users Bulk Properties Editor could prove to be a realistic alternative.
This software is not reviewed yet.
Consolidate various list items into a single grid view web part; Create public or personal view for a SharePoint list collection to filter, sort or group information. Create and manipulate items in SharePoint list collection as in default list view
Quickly cross-reference data from a list or site then apply a combination of filters to reduce the options presented in menus to eliminate error from incompatible values. Support look up information from 'Date and Time' and 'Number'columns.
Users can add one or more filters to build multiple cascaded relationships for the Cascaded Lookup column. And no limitation on number of cascading levels.
Reduce the administrator's workload by empowering users to change their passwords through the Password Change web part, and reset their passwords through Password Reset web part.
SharePoint Column/View Permission provides further protection on list columns and views than the SharePoint permission system does. Using it, you can safeguard the confidential column contents from access and edition by unauthorized users.