May seem like a weird subject to rant about, but I prefer to think of it as a “very specific to fantasy” subject. Or maybe those weird dynastic romance novels that marry half a dozen sisters off.
….a.k.a not letting it take over the story.
1) Don’t push every single relationship at your readers.
A family tree in the front of the book or at the back can be very helpful (I would be lost in Martin’s A Song of Ice and Fire without them). So can mentioning a few names when you need them. Maybe we learn the names of the protagonists’ parents in the first chapter, the names of his grown siblings a few chapters later, the names of his cousins after that, and so on.
What I really, really hate is infodumping that’s supposed to introduce you not only to the Hero and Hero-Father and Hero-Mother, but Mrs. Hero, all of Mrs. Hero’s relatives, and all of Hero’s cousins to the second degree. You know you’ve read at least one fantasy book like this. The protagonist is usually watching people come into a room for a wedding, funeral, or other ceremony, and noting the presence of every relative by name, degree of relation, eye and hair color, and heraldic symbol.
*Limyaael pushes down the evil memories*
Ugh. Yuck. No. Not all of these people are going to be important to the story, and even if they are, this is another case where the writer is going into “As you know, Bob…” mode. The protagonist already knows all these people (sometimes scarily well). Why would he or she stand around and think about them all? Find some other way to deliver the information. Small personal meetings are best, and mostly as they become important to the plot. Even then, I don’t think the difference between third cousin and second cousin once removed is as important as a lot of authors think it is. You can easily mention that this person is a “cousin” and let the really interested reader work it out from the family tree.
2) If you introduce a tradition of repeating names into the family tree, it’s your responsibility to keep track of them.
If you have six queens who were all named Agatha, then it is your task and no one else’s to mention whether it’s Agatha I or Agatha V you were talking about. (There are readers who will gleefully track down every mistake and mail you about it, but you shouldn’t rely on them). You should also not get them mixed up. If Agatha II was alive a hundred years before Agatha III, you can’t say that it was the second Agatha who built the drainage ditches if that was the third one’s main accomplishment. Minor details like this can and will screw up your whole story if you let them.
Be equally careful with names that resemble each other (such as Tyera and Tyrena). The royal family might easily have a tradition of naming their children with a certain letter or combination of letters. The Targaryen family in A Song of Ice and Fire has a lot of members with names that have “y” and “ae” in them (Rhaegar, Viserys, Aegon, Daenerys). But once again, you have to make sure that you’re not scrambling them. And please, for the love of little green apples, don’t name two royal siblings appearing in the same story with the same first letter. Martin very wisely didn’t; the three royal siblings of the present generation were Rhaegar, Viserys, and Daenerys, making them easy to tell apart. There are other royals whose names do start with the same letter, but they’re mostly dead, not major characters.
3) Know the birth dates and death dates of your important family members, and keep them reasonable.
Yes, this involves math, the horror of it. Do it or suffer from a horribly mixed-up family tree that will strangle some of the stories you want to write.
For example, say that you write about Princess Ortura being born in 1234 Dreadfall Reckoning and dying in 1264 Dreadfall Reckoning. This might make sense if your characters have the typical medieval lifespan or if she died in childbirth or of disease, but if everyone else in the family tree lives to be in their eighties, there’s a slight discrepancy here. Will someone notice? Oh, yes. But it’s your task to notice first.
Now, you can make this work for you and sprout a story. Perhaps Princess Ortura was murdered, and her family is covering it up. Perhaps she ran away, and no one’s sure she’s really dead. But you have to have an explanation, if only for your own sake. There’s a temptation that comes along when it seems as though too many of your characters are living about the same length of time, and that’s to just randomly cut their lives off. But you, as the author, cannot succumb to randomness here. Ask yourself hard questions about what causes the death of all your major characters. As I said, it can be something entirely mundane, but you need to know.
Also remember to keep the births of your characters reasonable. If you’re using a typical human gestation of nine months, three children born in the course of a normal year are impossible unless they’re triplets or one set of twins and one single child. Yet I have seen family trees that tried to do this. Please. You might have a medieval society where women are expected to bear as many children as physically possible, but she’d still have to take nine months to have them unless every one was months premature and still managed to live. She’d also be more likely to miscarry or stillbear if she was having that many children, and many medieval children died in infancy. And any human woman much past the age of 32 is going to start having problems with pregnancy.
Bottom line: Respect your dates. Some things can be twisted and broken in the course of a fantasy story. Birth dates and death dates are some of the much harder things to twist and break.
4) Decide on rules of inheritance.
This is especially important if you’re doing a royal family tree, but it needs to be worked out in noble ones and families where a political or magical office is passed down genetically, too. Pop quiz: If your current monarch dies without children, who does the throne go to?
If you can’t answer this in an instant, you need to go and have a long, hard look at that family tree again. Usual recourse would be the siblings of the dead monarch. If you’re using medieval rules of inheritance, then elder siblings would have claim before the younger ones, and male ones before the female ones (and probably the children of the brothers before the sisters themselves). If none of them are alive, then their children will suffice. If none of them are alive, then you need to go back to the previous generation and start looking for first cousins, then second cousins, the descendants of the dead monarch’s aunts or uncles. And all of this needs to make sense, so that if someone asks why the inheritance has settled on an obscure daughter of the line rather than a politically prominent and well-liked son, you’ll be able to answer.
‘S a bitch, isn’t it?
You’ll also need to consider what happens to widows or widowers. If your king has an infant son and dies, who becomes regent, the queen who is the boy’s mother but not actually a descendant of the royal line, or the king’s brother whose relation is more distant but who is royal? This also needs to make sense. If you have a political fight going on, then you need to know what kinds of claims either side will make, how willing they are to enforce them, and what other powers (like a royal council or the king’s other siblings) are in play.
And what about bastard children? And half-siblings? And mistresses or male lovers outside of marriage? And what happens if the rightful heir is too old or sick or otherwise unavailable?
All this needs to be done and made intelligent before you can actually write that this simple peasant girl is, gasp, royal and the next queen.
5) Be careful with royal marriages.
If you declare that two royal families are related through intermarriage, that should show up on the family tree. (This is another detail that a lot of fantasy authors love to throw in, and then forget to actually write down anywhere in the all-important genealogy). If someone had to marry the child of another royal family or a rebellious duke in order to calm a war, then know which marriage that was. The spouse so brought in should have an appropriate name, especially if these are two different countries with two completely different languages and cultural traditions. He or she should live an appropriate amount of time. If they die early, explain why. If they pass an unusual trait on through their children, another device beloved of fantasy authors (“Your great-grandmother was the last of the witches…”), then make sure that trait is one that they have a reason to possess. I’m immediately suspicious when the heroine has violet eyes, her great-grandmother had violet eyes, and yet no one in the country the great-grandmother came from or the family that bore her has violet eyes. It’s another excuse to make the character Special.
6) Be aware that changing one thing in a family line, especially near the beginning, changes everything.
A lot of fantasy authors like to make references to dead characters in the royal tree who never appear in the stories, like the Queen who founded the royal line. However, sometimes someone writing a story will get a new idea in the middle and go back to rewrite the story that way. Instead of a warrior Queen founding the country, it was now a simple wandering monk.
And this would be all right, except that just changing “Queen” to “monk” isn’t enough. Everything has shifted.
You’ll need to catch references to “foremother” and change them to “forefather.” The sex of that first spouse will have changed. The death date will probably have changed. The birth dates of the children will have to be adjusted. And once you’ve done that, you’ll need to adjust the age at which they married and had children, too, just so that you don’t accidentally have a nine-year-old with three daughters. And so on down the line. And probably the royal line’s tradition of war and heraldic symbols have to be changed, too.
Don’t screw casually with the family line. It will screw with your story in retaliation.
Genealogy is a pain, but leaving it up to chance will enslave you to that pure chance more quickly than almost any other aspect of a fantasy story.