I'd say that Sadism is highly likely to be present with families that have NPDs...I've been researching a lot about this recently upon my discovery that my parent is a Narcissist.
Plus there are two types of it. They are very different at home. All my life I thought it was normal. Here are some links...it's cut by parts but I hope you'll consider reading. Might help.

Introvert Narcissists are More Dangerous – Part 1 -Introvert Narcissist part-1
Introvert Narcissist at Home:Watch Out! – Part2 -Introvert Narcissist Part 2