After werewolves pack installed all mermaids turned into Werewolves

@Sabirah are you using mods/cc ?

@Sabirah Likely that an outdated mod caused this then.

Did you save that way ? If so, I would try loading a backup and remove your mods, If not, leave the game without saving and remove your mods.

If it's fine without them, you need to find the culprit

@Sabirah If you saved them that way, they're probably stuck. You need to load a backup.