If you must use an apostrophe, it must be because the name would actually sound different without it.
For example, a name like O'Donnell is pronounced Oh Donnell, as in 'Woe' Donnell. Without the apostrophe, it would be Odonnell, which would sound like O as in 'Odd', then Donnell.
Whenever I use them, I think whether they'd actually sound different if an English speaker was speaking it. Never mind the fictional language or culture, the book is being written in English, so I'm thinking in English context. Apostrophes should be treated like chores in a household for writers, avoid them however you can, use them when you absolutely must for the sake of what story you're trying to convey.