- Grandpa is stated to be a Republican, but he's usually at odds with the family, with his occasional adherence to the class system he grew up with in The Old Country and more conservative ideas, while the rest of the family who tend to emphasize social responsibility, with Lily actually working outside the home and refusing to let Herman as patriarch always have the final say.
- Gomez of the show has voted Democrat, but in the comics they are parodies of the conservative rich who tend to follow a class system and see themselves as the true Americans. It's possible the Munsters are conservative Democrats and the Addams are liberal Republicans.
- Herman and Lily adopt her and hence why she is called Marilyn Munster instead of her own father's surname.
Her brother is a werewolf so unless her mother- whoever she was- married a werewolf guy herself, chances are, it's actually her. And Eddie has to get his heritage from someone (highly unlikely Lily cheated). You can see some slightly vampiric traits in his appearance, so perhaps he got all his looks from his maternal side and nothing from Herman's. It happens sometimes.
Plus, Grandpa is also exactly the kind of guy you'd expect to be okay with having wives of a different species. And he's had hundreds; I'm sure he didn't stick to only other vampires.
Lily's sister is quite likely a monster herself, given that nothing is ever said about her "unfortunate" looks the way Marilyn's are. Perhaps she fell in love with a normal man and Marilyn took after him. The fact that Marilyn's looks puzzle the family suggest they don't know where she gets it from, so possibly her mother didn't tell anyone what her husband really was for fear of discrimination.
As stated above, Grandpa mentioned having hundreds of wives. You know Lily has at least a few other sisters and brothers out there besides the only two we know about. They're all somewhat similar in personality (don't care to wear all black or be frightening like traditional vampires; are sweet and doting; none of their mothers are seen; Draculaura and Lily both like tall, athletic guys; Sibella and Lily don't understand why people are afraid of them but are still very friendly and accepting of those who don't look or live like them.)
They just like scaring people and pretending to not know why others run away screaming because they're Trolls.
The Munster Cast podcast threw this one out, and it makes sense. She looks like an ordinary if very beautiful woman to us, and has no trouble at all attracting men. Chances are she IS a monster, just not a scary-looking one like her family.
She shares the exact same goofy, punny humor as them, and has their same Perky Goth personality that they have. The Munsters (and their Dracula side) have loads of relatives; who's to say Elvira is not one of them?
She never questions her family's weird customs even though she mingles with the "normal" world more than they do as a college student. She gets the norms of both monsters and humans, but still doesn't quite fit in with either, as she clearly misses cues from people or misinterprets their emotions (she isn't afraid of her family or their haunted house, so why would anyone else be? They must be scared of something else, or bad mannered!), and doesn't understand why people think she's weird (it's not her, but she doesn't know that). It's because she follows all the rules, so she doesn't understand why things don't work out when she does what she's supposed to do.
He gets hyperfixations, seems to struggle with focusing, but can work extremely hard when he gets the energy and drive to do something, his anger seems to be akin to meltdowns when he feels overstimulated (accidentally breaking things), and his fist smashing/aem waving can be seen as stimming, which many folks with ADHD do.