I have already answered the topic but I'm kinda updating it. I haven't played the Goths myself but they have been involved in other things and spiced up my game.
Mortimer. My "main" sim Axel accidentally started a romantic interest relationship with elder Mortimer cuz I forgot enchanting introduction was considered flirty. Because it was Mortimer and not some random boring townie, I just decided to roll with it instead of ignoring it and thus Axel's characterization changed from faithful to faithful-ish, someone who flirts around but never goes further than that as long as he's in a committed relationship. His wife btw repeated the same mistake later (how was I supposed to know "Impress with video game prowess" in contextual menu was romantic?) so now I RP them having this mutually open-ish relationship in which flirting is fine. So, thanks Mortimer, I have had way more fun with the game because this opened a door for many future chuckles.
Mortimer later died of old age, thanks to me still being stuck in my ways of playing TS3 and keeping the aging on for everyone (I kinda regret this now), but Axel had no qualms flirting around with his ghost instead. Mortimer's family didn't seem to mind.
Sadly though, just yesterday I noticed that since I had a longer pause from visiting the Goths, Mortimer's ghost now seems to be gone from my game thanks to the stupid relationship culling.
Bella, Cassandra, Alexander. They have all aged up. Bella is an adult while Alexander and Cas are young adults. Alexander is pretty hilarious with his Erratic and Gloomy traits. He likes to get naked in the rain and then forgets to put his clothes back on. I'm actually considering pairing him up with one of my sims though haven't decided with whom.
I had switched back to my TS2 type of rotational play so they stopped aging and pretty much just chilled around doing nothing... minus Axel occasionally poking around. At one point, when Mortimer was still around as a ghost, he half-accidentally made Bella and Cas smitten with him too (Alexander was passed out on the floor, I'm sure he'd have joined otherwise). I was testing the whole Vampiric Allure thing while having no idea how it worked in practice. I thought I had to target a specific sim or something. Nope.
Later someone in the forums actually made me realize the Goths would make great vampires so Axel decided to make them all his offspring and finally be done with the whole Vampire Family aspiration.
Bella's default dark form was pretty rad (minus some stupidly random outfit) so I left it as it is and only added back the outfit and makeup (and jewelry once I remembered). Meanwhile Cas looked like a Klingon. I still haven't decided Alexander and Cas' final look but I gave them all the same eyes for that family vibe.
https://i.imgur.com/sUR2eZL.jpg