That's a lot of questions for a single post, @Andrew Caldieraro, but here goes with at least a couple of answers/suggestions.  

Wife and I are getting ready to make first major purchase and I wanted to share something that happened.After many months, I finally convinced my wife that the road to success will require us to downsize from our nice $250,000 single-family home in North Central San Antonio into something more modest, like preferably a live-in duplex or four-plex.

And you need every single one—if ONE of them refuses, this strategy fails.

I had also read that a single member LLC ( with foreign nationals) is disregarded in the US and subject only to personal income tax.

There are some allowances and tools, like single-premium immediate annuities to hang on to more of the money for your mom. 

For resale in a B - A class single family residential neighborhood, definitely. 

They tend to to just manage their own ONLY.

The guy who was interviewed did exactly what you are talking about...bought a couple of single family homes and rented out the rooms which helped him to be able to continue buying more rentals.

I am now about to close on a single family rental property in Philadelphia.

I am looking at single family homes, student rentals or duplexes at the moment.