If there is anything left over I would return it, if not and they owe more I would probably consider forgiving it vs. suing them to try not to provoke them filing a suit as well. 

Moreover, some of the most important historical information is in local building department/fire department/health department files.

The one you most closely align with is if you intended to rent the house for three years or less, but to qualify for that you would have had to file for an exemption prior signing the rental agreement.

I know with syndications you need certain legal documents in place, does this apply to an investment group with under 10 investors, would I still need to get a securities lawyer and file with the SEC?

The amount you listed at $4300 should be deductible, whether you're filing jointly or separately as you're under the limit for both for 2021 tax guidelines- $10K filing jointly and $5K filing separately. 

The buyers for their current home just filed an 8-day UE b/c their funding hasn't yet arrived (bank outside of US). 

I've helped with 3 separate companies that do crowdfunding so very familiar with SEC Reg CF requirements and accounting needed for it long before you have a video or pitch deck decide it you are going for a Public SEC-registered CF filing you can raise up to $5 million per year.

We filed a law suit and clouded the title of the home so he could not sell. 

We filed a law suit and clouded the title of the home so he could not sell.

We filed a law suit and clouded the title of the home so he could not sell.