If you really want your story to reach others in your extended family, an index is critical. Many researchers won't even browse through a book without an index. Just think how frustrated you would be to find a book you think might be on your family, but have no means of finding where your branch might fit in. Source citations are also essential. Otherwise, the reader has no way of knowing that the book is not a work of fiction.
Every good researcher knows to leave a trail that others can follow to verify the research.
Make it easy for the generations who come after you.