Yes, it is in your best interest, and it is your responsibility by law, to keep your property "habitable" which I guess depending on interpretation could include keeping your properties pest free. 

If you're ok with that, then no rezoning required, but I interpreted your comment to suggest you want a subdivision as in a neighborhood.

I interpret that to mean that person is hard to find, which means it's unlikely anyone else has approached them so if they're interested in selling I can [hopefully] be the one to get the lead. 

Consult your own attorney who can review the condo association bylaws and give you an informed opinion as to whether or not the owner's interpretation of exclusivity is correct for your specific circumstances.

This is very different from my interpretation from listening to the BP Podcast and reading Investing in Real Estate With No (or Low) Money Down.

He seems to be trying to bull his way through the situation and force my folks to move the tank based on his interpretations of the legal technicalities rather than trying to negotiate.

But I've found that "interpretation"  really varies among local district judges.  

Example: Lease says -'Tenant agrees that upon non-payment Landlord may self-evict Tenant after 10 days' - Tenant agreed, Landlord agreed, a there's even a written instrument ---- Self-eviction still NOT legal if Tenant protests; because your Lease can not supersede the law and that law is interpreted by a judge and that judge may actually find you, the Landlord, as trying to circumvent the law and there may be real repercussions from doing so. 

I hope this is not interpreted as a solisitation I know that is against the rules but I do have a question on my primary residence.I have had problems in the past securing loans because of my lack of W-2 income.  

@James D Malone was correct in his interpretation of my comments.