The only thing I'll be sure to say is that lalafells don't really have surnames! Siblings sometimes share a syllable or two of a name (like the "Coco" siblings in the THM story), but the second name is based on the first; it's not familial.
So my lalafell, Caidenden Caiden... her "surname" is Caiden because her first name is Caidenden, not because she's from a long line of people called Caiden.
Otherwise you'd end up with a LOT of lalafell with exactly the same name and no way to differentiate between individuals beyond a "Sr/Jr" suffix. xD
Something you could work with instead is an "epithet" - lots of NPCs have them, like Aymeric the Blue and Karasu Redbeak and all that. These NPCs have surnames as well (Aymeric de Borel, Karasu Kanshi) which usually tell you something about where they're from or who raised them, but the epithet tells you something about what they do or what they've chosen to be like.
So my lalafell, Caidenden Caiden... her "surname" is Caiden because her first name is Caidenden, not because she's from a long line of people called Caiden.
Otherwise you'd end up with a LOT of lalafell with exactly the same name and no way to differentiate between individuals beyond a "Sr/Jr" suffix. xD
Something you could work with instead is an "epithet" - lots of NPCs have them, like Aymeric the Blue and Karasu Redbeak and all that. These NPCs have surnames as well (Aymeric de Borel, Karasu Kanshi) which usually tell you something about where they're from or who raised them, but the epithet tells you something about what they do or what they've chosen to be like.