But .. he does NOT (apparently) own the Florida residence, and that puts the entire situation into murky territory.
As a beneficiary of a trust, he may indeed be considered as a partial owner of the property held by the trust. That is why I suggested going in with a copy of the actual trust document so the agents there can see for themselves and possibly make a determination. Sending a letter is fine, but without seeing the documents there is not as much potential for a positive outcome. And I wouldn't go so far as to send them a copy.