Just some ideas. I call on experienced NYC investor @Llewelyn A. to give this any validity with local laws.
Take over the house subject-to his first mortgage. Create the seller financed piece as a $50k second lien mortgage at an agreed upon rate, and explain that you’ll pay down the $50k note to them (which they’ll be earning interest on) and after a year or two (when you can shore up your credit/income requirements) you’ll get everything refinanced into one loan so that the seller and the original lender are paid out.
He’ll collect interest on his $50k before being cashed out in the future, and you won’t have to go through a bank. I believe there’d also be some benefits to the seller by collecting $50k over time instead of being taxed on it all at once. It’s all about selling the benefits of this structure, and it works best if they don’t need all the cash today. If they need some cash, give them a down payment on the $50k seller financed second mortgage.
You’ll have to take on payments of their first mortgage. If that first mortgage is current, and you continue to pay it down, the original lender should have no reason to trigger the due-on-sale clause, but this is something that can happen. Basically the trigger is that the lender could say “this house is being sold via this “subject-to” transaction so we want our $550k today.”