Spend the $ to have an attorney investigate this a bit and make whatever claims are available. 

For tax purposes you'd have to investigate or ask your CPA.

I would re assess your long term goals and investigate the regions you are contemplating.

I believe you should investigate "adverse possession"

I'm not sure about the lending process in this proposed scenario.We will further our discussions with the tax pro, as well as likely hiring a business attorney to ensure everything is nice and tight, but in the preliminary stages any (non-legal) advice would be appreciated!

Unless you have access to commercial databases that contain SSNs, you best bet is to hire a "skip tracer" or a private investigator. 

Your right on the money in my books with what you need to bring to table but any doubts look at your good faith estimate from your lender for the loan or ask for a preliminary HUD-1 form.

I asked there are more than 100 airbnb in that zip code, and many have multiple listings, so they are not using them as primary homes, she told me they don't have enough people to investigate every property, but if they get complaints, they look into it one by one. 

I would investigate Stessa, TenantCloud, Avail, or other property management software.

If you travel, but you have not identified the property that you actually want to buy yet and the cost is considered investigating cost.