…and you’d have the Malfoys all over again.

Perfect evil is impossible. There would be no family.

Take Aunt Bella (please). Pure evil. Even if she could, by some means I can’t imagine, manage to produce a son, he would have been separated from his mother by Azkaban when he was a baby. Send him to someone equally evil? No such person would take him. Give him to someone as mean as the Dursleys? Then we would have to feel sorry for him. Send him to someone partially evil, but a decent mother? That’s Narcissa. Now we have the Draco twins.

Later, when Momma busts out of Azkaban, she still couldn’t have reclaimed custody of the kid (not that she would want to) because she was on the run.

No matter how you worked it out, you couldn’t have a family that is more evil than the Malfoys and still be a credible family.