Another option is to get an interest only loan, which reduces the payment amount and thus allows for more cashflow.

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. 

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.

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

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?

Absolutely not, but every investor should see the red flags and consider their alternatives before moving forward. 

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.