Maybe the threat of an eviction on their record will motivate them to pay the past due and start paying on time.

Your threats won't matter, the consequences won't matter, their priorities are different than ours (hence the poor financial management) so expect them to worry about keeping to the contract last. 

Again I doubt the LoI meets the prima-facie requirements for a contract and thus as Robert just pointed out, it won't be binding and despite possible threats won't be brought to court.

I have a very nosy neighbor who has been very angry with the noise and work on my house. She has complained about everything from the contractors parking their cars in the street to noise after 6pm. Two issues with th...

Remove the threat to the family finances.

I would sell in a heart beat....Downtown San Jose is one weird spot in super hot Bay Area real estate market.... not many jobs, most people would NOT live there, rent or own....Vacancy is a very real threat there...

Luckily it stayed put at the last-minute, but it was a threat. 

Zillow estimates (all AVMs for that matter) are crap and a threat to the balance of the Force.

Don't make threats, just inform. 

My 2 favorite CPAs are on this threat already: @Linda Weygant and @Brandon Hall.