I recommend that you find a trusted or recommended Mortgage Loan Originator (MLO), who can give you options for property-based loans (mostly investment loans) and they don't use your taxes but the P&L of the property.

(Even went beyond the second page of Google.)I have an investor who wants to partner on a deal by providing a loan for the down payment.

If you're purchasing a single family home you can use traditional financing like you probably did on your house or you can do a commercial loan.

Understand what you are investing in....is it a secured loan, unsecured loan, membership interest in an entity that deploys capital like a feeder fund or direct membership interest in an entity that is the deed holder? 

I went from a 15 year loan to a 30 year loan, locked in my interest rate at 2.85%, pulled out $111K in equity, and lowed my monthly mortgage by $20 per month. 

If a HELOC isn’t an option, alternatives like a home equity loan, business line of credit, or a DSCR loan could work depending on your situation.

Credit pulls for the same type of loan within a short window (usually 14-45 days) are treated as one inquiry, so your score should be fine.

The deal will leave the seller at your sons mercy for decades (the life of the loan).

I have been doing these type of loans for 30 plus years and buying foreclosures since the late 70s.. seen it time and again  ..

FHA LoansIf your down payment savings and your credit score aren’t where you want them to be, an FHA loan could be your pathway to buying a home.