Hello and thanks for using Just Answer.
My name is ***** ***** am happy to assist you with your enquiry.
The Agency agreement signed by the relative is null and void- the relative has no right to sell the property. It would have been the same situation had I walked into the Agents and signed the Agreement!
The Agents can't, therefore, demand that the same terms are signed by the Executor.
I trust this assists and sets out the legal position.