I've been reading a book and the author outlines several key metrics to study in order to know your market:1.

In this post, I’m going to outline the process for all my fellow newbies out there.

Explains eligibility for federal programs for refinancing and modification of mortgages, including a self-assessment toolQuestions and Answers on Home Foreclosure and Debt Cancellation, IRSProvides critical information on the tax consequences of foreclosure and debt cancellation, with links to formsWhat Happens When the Bank Forecloses, MassLegalHelp, 2013.Outlines the steps from a missed mortgage payment through the foreclosure auction.Print sourcesMassachusetts Mortgages, Foreclosures and Workouts , MCLE, loose-leaf.Short Sales, Deeds-in-Lieu & Receiverships , MCLE, 2010

It outlines much of what you're asking.

No direct experience with a small multi-family lease option (LO), but the process is the same regardless of whether it's a SFH or a 1000-unit mega-plex.I'm going to outline the basic format of an LO, in case you're not familiar. 

To be clear when you purchase a note and mortgage, you’re buying the debt that remains to be paid on the note, which is secured by the asset outlined in the mortgage.

I do, however, recommend making sure all expectations and responsibilities are very clearly outlined and who's getting what for their contribution.

Hopefully your lease outlines that they need to take reasonable care of the property. 

or should I write up an addendum for their leases outlining the payment plan? 

You should be walking the appraiser through the house, outlining all the things you did.