Seller financing questions

[Griffin Gartner]

Hi everyone! My title might not be totally accurate, but here is my situation. I recently bought myself a home for personal use (I am remodeling as I live here, to eventually turn it into a rental!). A close friend of mine and his mother finished a flip house in August, but have been unable to have any luck selling it. I am very interested in the house they have for sale, but since I am only one payment into my mortgage on a single income getting a second mortgage isnt currently an option. To cut to the chase, I am exploring using the seller (my friends mom) to finance the purchase until I can cash her out with a conventional mortgage down the road. I get the basics of how it would work, but how can I make an idea into something that would work for both parties? I am especially inexperienced when it comes to the legal aspect, as I assume we will need a contact between both parties. I am open to any and all advice!