I've definitely bought bound books that I enjoyed less, and I thought while I was reading them that they should've been bound and gagged.

Exactly.

What I suggest is the issue here is the lack of publication of the novel. That's where the rubber meets the road, where the work is validated. Publication is the consummation, the act that sets many things into motion. The person who owns the manuscript at this point, owns the novel. He can protect the copyright by publishing it, however he wants. He's not interfering with a published work. If the family sold the manuscript, knowing or unknowing, they still don't own it, and don't have a claim on the copyright or proceeds. I dare say that if someone were to take something like personal letters and publication is pending, then the original writer or his heirs could at that point negotiate with the one who wants to publish, because there are certain things understood about private communications such as letters. I think they are possibly different that something that is called a novel.

If a work is old enough to be out of copyright, then anyone can publish it, and they can protect their version, though someone else can also publish it, and protect their different version. The annotations, introductions, edits, etc. The scholarship that goes into the text, for example, makes that book a separate work, and the copyright clock starts all over again.

It's not like I don't know what I'm talking about. I am sure there are ways the family could impact the publication, were they to learn of it. They might be proud to see it happen, they might not. Someone might claim that it is an assassination of the character of one of the author's family members, for example, and threaten to sue the deep pockets of the publisher. So you as owner would have to decide if this is a threat or a bluff. I had a friend who was pilloried in a novel by a disappointed lover; after the affair ended badly she wrote a vicious story set in their city and workplace, he was thinly disguised, assuring that all would recognize him. Rather than face the humiliation and the breakup of his family, he took his own life when he learned a publisher had accepted it. His wife confronted the publisher, once she knew the whole wrenching story, and the author was compelled to change some of that novel, particularly the part in which she named and described his children. She still took a lot of swings at the wife. My friend was not such a good friend after all, I found, and he was mentally ill. He had created a golem of his wife to scare the world away from his family. They had never met her, yet detested her, and would not warn her about the novel. My friendship predated his bad behavior, and I was the one to wade in and alert the wife, once I learned of the manuscript from one of his coworkers. So, a book about death and destruction? You may want to do a little fact checking before you chuck it over the transome. The woman who wrote the novel had a contract, it was published but never promoted and was remaindered so fast I'm sure it made her head spin. She hasn't appeared in print since. (Just so you know the rest of the story.)

SRS