Menards is our closest option, just a couple miles away.

Just another exit option that you could offer him!

It's important to thoroughly research the auction process and potential financing options before diving into purchasing the 6 unit building.

If you want to try and meet them halfway you can offer them 2 options in my mind.  1) continue to pay the lease until you can fill the space, AND until the rent commencement date of the next tenant. 

Also I am having more and more difficulty finding insurance companies service STRs.My agent recommended a visitor covering option to my regular insurance.

Lending - if you have $100,000 liquid and are not afraid to lose some money or to wind up with a house you lent upon that had to be foreclosed that might be for you.Single family houses have a lot of options.

Just a followup - if buyer decides not to buy furniture, but tenants are still on the lease for a furnished apt. what might be my options at that point?

They have a few options including paying off the plan early and completing the chapter 13 and then selling the property. 

If the problem persists, you could look into soundproofing options for the ceiling, like acoustic panels or even just thick rugs or blankets hung strategically.

TBH i think your best bet would be to have that 10% - 15% 'jr. debt' be from cash-out on another property, if it's an option.