I have been able to find a couple of options for this setup though, they just require separate leases for each room and sometimes 2-3 months of rental receipts as well. 

Kelly, you have many options.

One option might be to explore adding air purifiers or filters directly into the system to help mitigate odors.

Seller was not willing to extend contract or accept creative financing options.

These are the options we are trying to decide between… thank you in advance!

I've found options in Costa Rica, but rates are in the 10% range.Does anyone have any experience or guidance on obtaining a mortgage equivalent to purchasing a 2nd home in the US?

I faced numerous hurdles and stressful moments, but I persevered and built a successful approach.To tackle this challenge, I recommend starting early by building relationships and seeking investors.

I'd like to move forward with option "b".

Sometimes cities will allow this, but it depends on local zoning rules.If neither option works, it might be worth consulting a real estate attorney to explore your options.

The "non conforming" lending options are actually called NonQM (non qualified mortgages).