Well as an example, I can tell about a few of my households, maybe they might inspire you. First, I have one sim/vampire household. There is my main sim Matilda, a vampire with the serial romantic aspiration completed, a bit of a baddie. Then her non-vampire wife (who gladly always offers her arm for plasma) and her boyfriend Caleb Vatore. So all three of them live happily together. Matilda has a bunch of vampire kids with Caleb (to fill the world with more vampires). They are very rich and have a butler, who gets often drained of plasma as well. It's a very fun and different household, I can tell you that lol
Or, I have also created Joker and Harley Quinn for my game and they just wreak havoc in the world. Both evil and in the villain careers. It's fun to play with them and just be the absolute worst. They have a dungeon where one of my sims from another household has "mysteriously" died, the Joker is the secret father of one of my other sims' child, etc.. Always if you want something bad to happen, you can make it their fault basically haha.