If I recall correctly, you
do need an active telephone line / connection for the All In One machines.
If your only "live line" is where the router is, is there a plug in option for a telephone, and if you don't have a landline number, how are you able to get online? Doesn't a phone line need to be activated in order to work? Are you using a cable line (ethernet type) and not phone? (sorry if I'm misunderstanding this)
I'm just trying to think of options to help. If the router can handle a phone plug in, maybe the fax cord can plug in to the router, for you to be able to send / receive faxes. But, you still need an active telephone line and number to do any sending or receiving. The All In One isn't an all in one if you aren't using all the functionalities. Faxes need an active telephone line or they can't do anything (if you're using an app on your mobile to fax, wouldn't it be akin to using your cellular data?).
Sometimes the machines come with all the software, sometimes they don't. You really have to look around in what the installation stuff is. However, there should be an option for the fax software once you put everything on your computer.
Nowadays, the machines have an app for smart devices, so you can download it to your mobile and do everything that way. Maybe there's an option to scan and fax through the Brother app on the mobile? Or, just scan to the cloud and send via email? I know the point of a fax is to send it to a phone number, so if you can scan the document and then email it to a fax number, would that work?
I remember before I left one of my latest jobs, they were working with a provider that received faxes to a specific folder on your computer, and in order to send faxes, you were emailing the document to a fax number. Your email became the cover sheet. But you still had to register this program with a fax number to do anything. I forget what the program was called, but it seemed to be working.
As a side note, my mother has a friend who has one of the fax inclusive devices, and she has a splitter device at the wall level for where her telephone line is. It's a little adapter of sorts, where her main telephone and fax line are connected to the one line. She just has to be called first and be told she's getting a fax because she's got to rearrange some things (and turn on the machine because she keeps it off most days).
The splitter looks like this:
View attachment 456065
I could be wrong and will happily admit to it.