Not for a single airbnb like you are seeking (you and everyone else) but because if you start a BNB or a guest house or a hotel, you can get 40% of your investment back in the form of a tax CREDIT that you can sell for about 90 cents on the dollar. 

Tell me - someone selling their home to your son, Subject-To - is this a person who has made good life choices? 

The low down payment house hack is the way to go.

Given your assumptions, you are not going to be able to get enough of a loan to fully cover the rehab, even with a hard money loan, so you'll need to pull in cash from elsewhere.One possibility is to have your mom sell you the house with a personal loan, not one attached to the property. 

These properties include different foreclosures and those that sell below their market value.

ADUs typically add value to a property, but it might not be at the same $/sq ft as the main house.

Have you considered all the tax implications of selling?

They might be willing to give different terms especially to a high net worth person that they can likely make money on cross selling.

Trusting what the franchise tells you is foolish.I can tell you this: there are companies selling leads to real estate agents all the time.

Get the house hack under contract and closed first.