Owner-Financing deal -- what pro do we hire to make it legal?

[Allie Dattilio]

So this is a multi-tiered question...

Working on our very first deal, negotiating with an elderly couple and would love to work out an owner-financing situation to then BRRRR. Any tips to negotiate, and keep it as simple and straightforward as possible for them to understand? (Especially when it seems a little complicated even to me)

If/when we get them to agree, what type of professional do we need to use to get it all legal and official? Real estate attorney, title company?-- who would be most efficient and cost effective? (Want to move quickly)

Hoping to get the house for $50k, would put $10k down. With perhaps amortized over 20 years? Still having to work out those terms once we have a better understanding of their motivations and desires. 

Considering we would like to refinance in a year or two to pay down the HELOC we are using for downpayment and rehab costs, and take out some equity for our next property, would it make more sense to offer a balloon payment at that time? How does refinancing work when its owner-financed?