Additionally, since my parents are nearing the retirement age, I'd like to prioritize low-debt, high-cashflow deals.

This eliminates the problem of increasing your debt and damaging your credit score.

Most lenders require proof of someone else paying the note for around 9-12 months so that the debt isn't counted in their DTI calculation.

But I’d’ also ask if the girlfriend is a legal US citizen?

https://www.biggerpockets.com/forums/51-tax-legal-issues-con...

If there is no debt service probably 30% is still going of the rent is still going to operating expenses which means that you only made about 480k or so. 480k rents + 800k property is the same 1.3million roughly.

Of course, every owner's situation is unique and factors like the legal entity involved, purchase date, adequate passive income that can be offset with the cost segregation study, etc., will need to be considered.

I've always been able to find my STR clients investments that are legal and whose numbers works. 

Just a follow up question, were you utilizing debt to invest, I have always been taught since a young age to try and not utilize debt (I come from a family of stock market investors, traditional business owners) where debt is not utilized as frequently which I obviously understand debt can be a very powerful tool and utilized in a great way its just something I want to avoid with my investments to an extent any suggestions for investing without debt or as little as possible. 

Eliminate debt, establish a budget, and save.