AI for author's family to use due to his recent passing?

Let me first say that normally I am not in favor of authors using AI to write books for them. However, I have a special circumstance. I am one of the editors for the Hamelin Stoop books by Robert B. Sloan. Dr. Sloan passed away suddenly on July 4 from a stoke, leaving his series unfinished. His children have vowed to pick up the torch and finish the series, but none of them are writers by trade. I am going to provide them with everything I have. The latest unfinished draft of the next book, all his notes, and an outline describing what we had discussed about what should happen in the series. I would like to offer them the option of using AI to help complete their father’s work. What AI program would you recommend for this? What are authors using? If they can feed the author’s previous four books into the AI so that it understands the writing style and then give it a detailed outline for what should happen in the book, would it generate a draft that we can edit from there?