I always played Cassandra as a sort of psychic little girl... Imagined if she had visions of all the Sims alternate realities and could see all the possibilities from every player? :P I could picture her asking advises to deceased family members and having some magic power. She was neglected by her parents (her father too busy with his experiments and her mother, too snob, she would have required a nanny). She ate a lot of cookies and chips since kids couldn't cook anything back then. She did her best to succeed in school.
Mortimer tried to be a nice father and water is plant, but sometimes did weird experiments and turned into a zombie and put fire to the house and burnt himself to death.
I always pictured Bella as a witch. I once made her a rich "pink" sister. She had affairs and once even became an actress. She enjoyed playing piano. She spent little time with her daughter as kids weren't "neat" enough. She was profoundly annoyed by the tragic clown. Her rare attempts at cooking often ended up in kitchen fire and she burnt herself to death many times...
ŦØŴŇ Ø₣ ŞŦŘΔŇǤ€ ŦĦƗŇǤŞ (StrangerVille):
Δ ¥€ŦƗ ƗŇ ŞŦŘΔŇǤ€VƗŁŁ€ (Sims 4):
Of Ears and Noses, a Grisby Legacy (Sims 3):