Client Accounts and User Accounts

WP-ers! Building my new business on WP. Got a great theme, and now we’re building the final back end. We will sign on individual business clients. Each client will have multiple users. The first client may have as many as 40 users. Each user will upload large (200+ pages) PDFs several times per month for us to “process”. Processing means organizing the PDF into different document types and then extracting data from some of those documents. So each user will login, upload a PDF, then come back and view the organized PDF and see / download the data from that PDF.

Users from within the same business client account need to be able to share access to the PDFs & data that they uploaded.

We’re looking for a plugin, so we don’t have to build this ourselves. We will manually create each client account, and then our client’s “Admin User” (assigned by us) will create the other user accounts within that client account.

Users within the same account can share their PDFs/data, but users from other client accounts cannot.

I’ve looked at Group & Membership plugins, but they don’t seem to fit, because they are focused on individual members, rather than a business client account with many users.

Help? Anyone know of a plugin that does this? Or, has anyone else here setup this type of hierarchy for accounts & users?

Thanks in advance.