Help them to see the merits of your cash offer.  

However, if you are unable to heed my warning, you must first determine if the opportunity has merit, as @Wayne Brooks mentions about equity.You can search on these forums for my PETIO format for researching these type properties.

- Will a signed affidavit from the siblings have any legal merit whatsoever, allowing them to sign off on the sale of the property?

http://www.zerohedge.com/news/2016-06-17/bursting-...Now I know Zero Hedge has a tendency to 'Chicken Little' every situation, but is there some merit to this one? 

I doubt spamming people with the merits of BP is going to make you the kind of connections you are looking for.

Im not saying your deal has any merit or not, just saying when you see seller financing on a property that actually is a deal..... get creative

Summarize the merits/risks/drawbacks of the deal for both seller & buyer:What is the current income, current value, terms of existing mortgage, optimal income, optimal value etc?

While the property made for a great place to live and a good rent free environment it was not necessarily the one I would have purchased solely on investment merits.

It's my opinion that ratios were established as a guideline for people who lack the ability to judge an opportunity on it's own merits.

Now whether or not that is true for everyone, the concept does have some merit.