The FaxFinder will be connected to a PBX with 9 DID numbers. Can we share these DID 's among many users?

You can share DID's by creating multiple entries using the same extension. For example, if the 5 users share DID 8965, create a separate phonebook entry for each of the users with their email addresses, but use 8965 as the extension for all 5 entries. Anytime a fax comes in on 8965, all 5 users will get it.