“Viking” isn’t a matter of heredity though. If your grandfather was a bricklayer, you’re not a bricklayer as a matter of heredity, you have to actually lay bricks. Likewise, if your grandfather was a viking, you have to actually go raiding and pillaging to be one yourself. Which is not something you’re likely to do if the king of France gave your grandfather an entire duchy in exchange for a promise to stop doing that sort of thing.