The biggest problem in this type of situation is the threat the board feels when making decisions because of a potential personal liability if it is shown they are negligent.

unfortunately, he only seems to respond to legal threats so the collection agency route is probably the best solution. 

I read an article that basically summed up That landlords should consider only whether the applicant poses a current threat to cotenants, guests, and employees.

Also you could buy the widow’s half of the property then threaten to sue the kids (hopefully the threat will be enough to get them to agree to take your money and sign over their interest.)

From day one she is trying to trying to make up things to get free rent by giving empty threats.

Don’t make waves or issue threats .

I use it here and on Facebook groups because notifications are one of the biggest threats to productivity.

My guess is that you'll find there's a gotcha on the vacation rental approach if there's a sublet restriction in place and the HOA can shut this down with just a threat letter leaving you with nothing to show.An HOA is a powerful entity with few restrictions. 

I like the threat of losing security deposit if they violate the showing stipulation.

The threat of calling the board is often more effective than actually calling the Board.