Is it illegal to copy ancient books?

There will be no infringement, and the copyright protection period in China is limited to 50 years before and after the author's death, and more than 50 years are not protected by copyright law. Of course, if we deliberately distort historical materials and discredit the contents of ancient books, it may involve the principle of public order and good customs in illegal civil law. After all, as citizens, we have the requirement of maintaining at least public morality, but this does not belong to copyright infringement, which is rare in reality. Judging from what you said, your brother should be fine, but then again, if writing is not creative and just draws on the wisdom of others, it certainly has no great future. Your friend interprets and processes the historical materials himself, so the copyright belongs to your friend. For example, The History of the Ming Dynasty basically refers to The History of the Ming Dynasty, so let your friends rest assured that it will be published.