Have you spoken to an immigration lawyer about your options? 

To leverage the equity for financing my next deal, a second mortgage seems like a more cost-effective option.

Question 2: if homes upside down on mortgage what are my options?

Bear in mind that the fiscal treatment of the two options in Mexico is different (withholding tax on the gross income with the fideicomiso vs cost deductions with the corporation).

Have you explored any of these options yet?

If that's what you're really after I would start with the basics of what kind of bank loans either residential or commercial are available to you - not saying this is the best option, but it's a good place to start.

The previous owner claims they never had the titles to these trailers, so that is not option. 

Quote from @Edgar Duarte: hi allI would love to get some perspective from your expertise, we have a property that we would have to sell in 2025 to avoid paying taxes on the capital gains, we believe we rcan sell it for $700K and get an equity of almost $500K after paying the mortgage balance, if we invest all of it option in index funds at 7% rate (standard com growth calculator), or in more rental properties as we are all here for, I can get the equity of around $900K.option B would be keep paying the house at 2.3% int rate while we have it in AirBnB and maybe sell it in 10 years for $900K, knowing that we would be paying taxes but it is not that bad still. or we can 1031 at that point?

What was the quality like compared to local options?

So brainstorm the different options then pull the trigger!