2FA on multiple accounts with one mobile phone

Xfinity developers, please fix the fact the 2FA requires a unique mobile phone number per account.  For most applications, I can associate the same number with multiple accounts. Why not Xfinity? My father's Xfinity account was recently hacked or Comcast made a mistake and linked an account with his that should not have been.  He doesn't text or have any other email accounts, and that's not going to change at this point in his life. I realized something was wrong when neither of us could access his email.  It has been taken care of now after 2 hours on the phone with Comcast Security.  This could have been prevented if 2FA was in place.  Months ago, I tried to set up 2FA on his account, so I would get a text me when someone signed on. I couldn't because my mobile was already in use for my account.  I have now set up a Google Voice number and associated it with his 2FA, but what a pain to need another number and not have the messages come into my phone's message app.

And yes, I have my account linked to his, but that doesn't have anything to do with 2FA notification.  

There are plenty of people like me who are in an eldercare situation where their parents have separate accounts, and we need to protect them from scams and hackers.  Please make our lives easier, not harder.