With the web, it may be piecemeal which can work for some individuals.After spending thousands on books, courses and seminars, I'd have to say it is the conglomeration of the information learned in the materials as well as the experience gained from applying these principles that has led me to where I am today.

Out of principle, I think you have the right idea.

But realtors are like many industries, it's the 80/20 principle with the best making the most by a substantial margin.

Or you can work out a new agreement with the owners and increase the principle by the amount that wasn't paid and increase interest a bit.

@Donald Lartson, I second @nnanurnyi anigbogu, The Book on Flipping Houses and the Book in Estimating Rehab costs, are really the Bible for running a successful rehab business.If there was ever an example of the 80/20 principle or the 90/10 thus would be one.80/90% of all the  wisdom contained in books for  running a successful rehab business is contained in these two. 

I understand how markets work and the basic accounting principles of real estate too.I am asking for any advice that anyone may have on this matter.

Yes, but its more on principle than a rule. 

While some of their points may be a little extreme, I think the principles are sound.

I would negotiate where 10% more of my payment buys principle/ownership.  

They are willing to put all payments of  principle and interest towards the debt.