I can think of a couple of reasons there may not be any taxable event here.

The seller's Schedule E is a good start since sellers usually don't overstate income nor understate expenses on their tax return.I do want to note that the bottom line on a Schedule E is not "profit", it is taxable income/loss.  

You've invested a year working on this so you can earn a commission which is highly taxable earned income

You are correct a refi is not a taxable event  It is a loan against equity.

So, let's say $50K is left in the company at the end of the year, that $50K will still be taxable to the shareholders (your parents).

For instance, any forgiveness of principal may create a taxable event for the borrower, you really need to disclose and have the borrower sing off on it, amongst other things.

If he is paying you $500/mo interest you will pay taxes on that and when he returns your $50k that is not taxable.

In your case this wouldn't quite fully work because at the end of the process you would be buying for 476 and sold for 485 so you would have a taxable event on the 9K difference.3.

Unless they are using it for the offset against strong taxable income, this is not for the inexperienced.

Then it shows up as a non taxable event.I used Sense Financial to set it up may Solo 401k and they were and are great.