If this is being published as a work of fiction, then you can use whatever name you wish. If it is non-fiction, and you use the executor's name, then the information had better be true, or you are begging for a defamation action. Truth is an affirmative defense to defamation. But you may be looking at a lawsuit, regardless. I guess you need to weigh that risk and ask yourself if it is worth it.
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By all means, the book should be "vetted" by an attorney experienced in publishing law and defamation, not only for protection from liability for defamation, but to make it publishable and marketable down the road. A publisher that might otherwise be interested in picking up the book if sales go well, will not be looking to pay an advance to take on a lawsuit.
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My colleagues are both correct. You need to have the publication reviewed by an attorney familiar with such issues. Regardless, you should expect to require the assistance of defense counsel (for defamation) after the book is published notwithstanding that truth is a defense.
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