Use of real people, long dead.
Question: While reading some other answers posted, I came across one talking about libel and mentioning real people in fiction, and it worried me slightly. I saw written that those long dead usually do not count, but I wanted to ask:
In a fantasy story I’ve been working on, I have it that two real, historical siblings survived a factual massacre, which in reality killed them, and are now immortal. However, one of them goes on to plague the protagonist for the duration of the series as the antagonist. It’s only a children’s/YA book, but you now have me worried that it might be slander, even though everything mentioned in the story is obviously fiction. I'd be stunned if this could hurt me, but I feel I need to ask now... Answer:
My understanding is that you can say what you like about dead people without being sued, since you cannot cause them financial harm by damaging their reputation.
But you'd have to ask a lawyer regarding whether their upset descendents would have a case (I'm guessing it's unlikely, unless they're still making money from their deceased relative's reputation).
Nonetheless, the easiest thing to do in this situation, assuming the siblings in question are not famous, is to change their names in your story.
If they are famous, and you've chosen them because of their fame, I'm guessing you don't want to deviate too far from their known personalities anyway. I mean, you're not planning to turn the ghost of someone like Mahatma Gandhi into the villain are you? If this is historical fiction, you want to teach a little real history to the kids, right?
On the other hand...if you are making a Gandhi the villain, since you're writing fantasy, perhaps you make clear that the story takes place in an alternate timeline where historical figures have different personalities than in real history.
Of course, if we're talking about the ghost of Hitler, no one will object to your portraying him as evil.