I think JT is likely correct. If they can demonstrate power of attorney for the deceased estate, then they would have the power to appoint themselves as proxy for the deceased owner if that owner’s name is still on the title documents.
Also, from JT’s quote, it seems that a person who is empowered to execute a transfer of the title, which might be the executor, can act as the owner and could appoint a proxy, which could be the heir apparent.
I think the chair of the meeting would want assurance from the Secretary that appropriate evidence has been presented before the chair would accept their vote. With such evidence (and levies up to date), I think the chair should accept the heir apparent’s vote.