>>It turns out this can be done using e-mail. In this case the client has a secure mail back-end (Exchange) and remote staff can use either Outlook or Outlook Web App (web mail) for a secure connection to Exchange... trick is to send a ZIP file as an attachment to each staff as internal mail (don't send to any external mail domain).

I know you're in Canada but even the US HIPAA specifically accepts emailed confidential files as long as they're encrypted with something better than Zipcrypto. So your proposed model has support. 7Zip with AES256 is secure until the content is unpacked insecurely to the local device (which breaches HIPAA if the device is then stolen fwiw.) Consider something like Veracrypt: once opened with correct password, a Veracrypt repository behaves like an extra volume containing files that can be read/edited without insecure local copies.