If we name someone other than our daughters as executors, that person cannot make a deal with you as the authority to sell the property passed to our daughters, the trustees, as the property is now in their hands.

Yes, you're correct about the unincorporated County area, so the County is the authority, not the City. 

I called the Houston Housing Authority and they said my property would get approved for up to $4313 as a section 8 long term rental.

I was hopeful that time would resolve or lessen the bad relationship that my friend has with neighbors and authorities.

Read and study Principles of Real Estate Practice: 6th Edition by Stephen Mettling (Author), David Cusic (AuthorOr a similar text.  

Anyone telling you there is, is either lying to you or, obtaining nonpublic information without the authority to do so.

The person at the open house has no authority to make policy changes and wouldn't pretend to do so.

First, the taxing authority seeking to collect the delinquent taxes (county, city, or state) will place a lien on the property (also called a fi fa or fieri facias).

As others have said, I would leverage the Housing Authority with these people. 

At the very least he should be reported to his agency or proper authority.