If they cannot afford it then talk to the bank about a short sale or let it go to foreclosure.

Ok, so I read and loved Avery Carls “Short-Term Rental, Long-Term Wealth”.

Most lenders will for try to send you down other roads first such as a loan mod or short sale, before they agree to DIL. 

Choosing a location near LA, accessible by a short flight or drive, will make it easier to check on your projects.

Quote from @Premraj Jeyaprakash: I'm exploring potential opportunities in short-term rentals (STR) in West Virginia, with a particular focus on glamping.

I don't think you know enough to consider real estate in the short-term.

Long story short, there seem to be huge differences in loan approval processes across the banks...

Yes we ask towards the top of the market, but I anticipate my holding times (which are in line as the short supply in my area is able to work for me) and build that in. 

Cost to build an ADU are high, however, so it may not pencil out in the short-term.

Although, with all of the trips going down to Texas, having been burglarized, and in an area next to an active trap house that was selling drugs on the corner... occasional gunshots in the distance..