Internet fax numbers are tied to user profiles with 8x8 Work.
To share this among a group or department, one idea is to create a user profile dedicated to a specific group (I.e sales fax) and assign a fax number to share.
You can setup email notifications as well to alert a group email or individual users.
Below you'll find a video that gives a general overview of Internet faxing within 8x8 Work which may help in designing this setup for your organization.
Internet Fax - 8x8 Cloud Phone System