Structuring Seller Financing

[CJ Pilon]

I am looking at a deal that i think is perfect for seller financed but I need to get a better understanding of some details. 

The seller is relatively young, about 50 , but is forced to sell her home because she is disabled and lives in an assisted living complex. Her intention is to set up an annuity with the proceeds from the home to provide a steady income going forward. While her parents have been helping manage her affairs, they are older and wish to put the funds on auto-pilot. It seems to me that seller financing will provide a higher, more secure return than nearly other investment strategy

I want to structure a 30 year  mortgage (about $100,000) that would pay the seller  4% to 5% per year. Because income security is important to the seller, I need to understand how I can structure this deal so the sellers are not put off buy the risks of carrying a mortgage. Specifically how do you manage a sale tto avoid an unscheduled  lump some payout, or the possibility of getting the house back.

While I'm asking, what else do I need to think about?