In order to achieve a more efficient — which is to say less time-consuming — maintenance of the database, neither this category nor any of its subcategories should be placed into category:aristocrats or any of its subcategories.
In other words, please treat knights and aristocracy as two separate things in the category tree.
In the DWU, and indeed in real life, there's a difference between a knight and an aristocrat. Obviously, Rose Tyler and Ian Chesterton are both knights, but neither could reasonably be said to be a part of the British aristocratic establishment. Knighthood does not confer aristocracy.