Read as much material as possible and go to some local RE meet ups.

Watch what you say and accuse on the internet.

@Steve CrispIf you meet the material participation guidelines and qualify for the short term rental loophole you should get a free cost segregation estimate to see how much you would benefit from the accelerated depreciation. 

In February 2020, the tenants in a unit on a lot she lives on vacated per a 60-day notice, after my mom discovered they've been subletting the house to internet strangers without her consent, violating the lease agreement.

I just provide DTV and internet.

You could argue that your property has not materially improved and does not meet the same value as the most recently sold properties.

See if any of them will allow you to use their address as a virtual location on the Internet.

From my research, I'm seeing $100-$150/sqft depending on complexity and material.

Just be aware that (1) you can easily do whatever it is Tardus is selling much cheaper elsewhere (2) Tardus special investments for members only are mundane investments available at the same terms to anyone with a computer and internet connection and (3) the strategy of borrowing from a HELOC to juice returns carries with it a much greater risk than is apparently disclosed. 

I too at first thought it odd, that they didn't have a big internet presence, though they've been around over 6 years.