At this time is there any funding, that I would qualify for, to ease the pain of the additional expense?

I miss the convenience and ease of use of TSP, in hindsight. 

I have shared the obvious answer that he would take the the house back, but I can tell he is still worried about having to foreclose.What techniques or messaging do you find effective to address these type concerns and put the seller at ease when trying to close a seller financed deal?

Maybe offering to help find a new place and pay the first months rent and security will ease the cousin out of your place and into another, so you can close on your preferred date.

To ease tensions, I am in a very grateful situation to where I have no debt (besides my current residence and rental) and bring in 10k of free cash flow a month, so defaulting on a HELOC pull of 27k is unlikely.

I do this because I'm passing on the goodwill that was extended me, making the tenant more at ease about signing a long-term lease, and I firmly believe that more owner-occupied properties in our up-and-coming Buffalo neighborhoods is a good thing. 

Added value to the deal by easing the back office operations for the business while servicing the loan.

You’ve definitely eased my mind about going with the gas boiler upgrade. $10k was about the quote I got for the wall unit.

Thanks again for the help, jumping in to the game can be very intimidating but the BP family sure does ease the anxiety.   

It is always good and should help ease your fears having a good realtor on your side!!