Should I turn Alexander Goth into a Merman?

In my game, merfolk, elementals, vampires, and spellcasters that drink a potion of immortality are all immortal. They are protected from death by old age, and I don’t age them past young adult.

In my story, Ember Zalrian is a Fire Elemental and Spellcaster. She’s immortal but her boyfriend, Alexander, is mortal.

There are a few story paths I’m debating on:

Ember’s older brother and Water Elemental/ Merman could offer Alexander Immortality by giving him the magic mermadic kelp.

On the other hand, Ember’s younger sister, an Earth Elemental/ Vampire could turn Alexander into a vampire.

Ember, herself, could brew a potion for Alexander and possibly turn him into a spellcaster.

Alexander could end up an immortal human after drinking a potion.

To contrast Werewolves from Vampires, I am not going to make werewolves immortal in my game.

Alexander can’t become an Elemental because the Sulani Mana trait is genetic and requires an Elemental Parent.

The main thing going for turning him into a merman is the world he lives in now. Alexander lives in Sulani with Ember, and Sulani is mostly water. Most of my sims in Sulani are mermaids or mermen.