It also would take forever to recover the initial negative equity position.  

I'm working with an agency in Mazatlan already and they posted the ad in the area of Mazatlan, Mexico.I feel this will take forever.

This was during the biggest run up in RE prices since FOREVER.

Interest rates are high relative to house prices, this won’t last forever.  

That approach will take you forever.

FHA is good, but you have MHP forever until you refinance. 

The other thing is whether or not you plan on living with your inlaws forever.

They stay online forever.

They got fundamentally sound real estate, with matching debt (10+ yr fixed rate) and budgets with the intent to hold nearly forever. 

I probably wouldn’t mention your third point - it makes it sound like you expect them to hold this note forever and I’m not very certain, but I’m guessing there isn’t a huge market for $100k secondary notes.Have you considered asking them to finance 90-100% for a short period of time so you can rehab and refi at a higher valuation?