Then we would make it clear for the guest to leave the key prior to checkout.

This was the rule prior to 1998 (I think was the date).

I would suggest buying a ltr and getting to know reliable construction folks prior to taking on a construction project.

Next year, I'd try to find someone on a 3-4 month contract prior to the holidays.  

Either yourself, or pay a GC a small amount to give you a bid prior to submitting your offer.

And if there are open permits that have not yet been closed, make sure the seller takes care of them prior to closing.

Do you know what repairs are needed PRIOR to inspections? 

I don’t think anyone will leave a bad review because they didn’t know you had a structural beam/pole in your house prior to arriving.

@Cathy MalmroseAll else aside, your son is essentially a landlord for this time and he could put together a lease agreement immediately (ideally with the help of an attorney), which outlines a security deposit in case of damages, requires the prior owner to obtain renters insurance, who pays utilities and any daily rent- especially a daily amount that’s high if they stay beyond a certain date.This would at least cover the primary points in a leaseback.I’m curious about when and how the sellers made the request to stay past closing that your son agreed to - was it just between the two parties or was the Realtor part of that conversation?

The Winter time is slow with how cold it gets here so if you want to sell you want to do it prior to Dec.