It seems that you use plural. It is good practice to use separate login accounts. That most likely means that the folder for the calibre library/libraries should be in a folder that is shared with other users.
I believe that a long path may be problematic. So it could be a good idea to create a new folder "books", "shared books" or just "shared" directly in the root, as BR suggests. That way you reduce the length of the path.
Also that folder could be shared not only between users on the computer, but also over the network. So audio books and the calibre library easily can be shared and copied over the network. Please note that it is NOT possible to run more than one instance of calibre against the calibre library at any time, and that it is NOT recommended to use the calibre library from a network filesystem. So copy the library, and don't use it directly from the network share.
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