I recommend getting a structural engineer to look at it, not a general contractor.

The IRS will require them to charge a “reasonable interest rate” if they supply seller financing.

The easiest way to structure this is to purchase the property with a hard money lender that will cover both the purchase price and the rehab cost and refinance the loan with a conventional or DSCR loan 

The plus side is the airbnb supply has fallen and we have noticed a HUGE increase in our gross STR rents, roughly 20% higher then a year ago.

How would you suggest structuring a seller financed deal?

The purpose was for us to fix up the property and to flip it.Ownership Structure: My aunt and I are joint tenants, each holding a 50/50 ownership stake in the property.

Since this is our first property, is it advisable to use a single LLC for both personal asset protection and holding the property, or are there reasons to consider a more complex structure?"

Any tips on structuring this with a secondary loan or financing approach?

We need guidance on how to structure our partnerships.

Quote from @Sean Regan:  I put this as a structural challenge in a scope of work.