Seller Carry, What Documentation Is Needded to Protect Both Parties

[Gina Francis]

Bigger Pockets Family! 

We we have a dear friend who is in a financial pickle and has offered to sell us his out of state 3 bed, 2 bath home for $290K (currently listed for $300K). Loan is assumable ($182K balance at 3.75%) and he'll carry the $108K balance at 5.5% with a 5-7year balloon.  Down payment is 20% on the 108K. 

We're looking at purchasing this as a family investment with my sons. 

We'll work directly with the lender to transfer the loan but are unclear on what documentation is needed to protect both parties regarding the terms of the "owner carry." I'm assuming we need to hire an attorney to draft up an agreement, but don't want to go into this blind. 

Grateful for any recommendations.