While writing Kaleb, I continually imagined him with a brother, although I didn't write them into his history. I wrote his family unit as far as siblings go pretty vague so one could be slipped in there if anyone had an interest in being related to him. I'm all for a sister as well, but the FCs I headcanon has his sibling(s) are both male. That being said, I am not too picky are strict about what his sibling(s) are like, other than (obviously) them being related to him in some fashion.
As far as face claims go, I envisioned his brother as being either Caleb Landry Jones or Elliot Page. I know both of them do not have the largest collection of pics, so I am not married to them being the FC. (Gatten Mararazzo [Dustin from Stranger Things who is always with Eddie, who Kaleb's FC plays] is twenty, so we could always make use of his brotherly pics with Kaleb's FC if desired]
- I am not picky on how close Kaleb and his sibling are. They can be basically joined at the hip or be has distant as two siblings can be.
- Maybe sibling got along better with dad and got more love and attention from him than Kaleb did.
- Maybe mom took sibling with her when she ran off to America.
- Sibling can even be Kaleb's half sibling with his dad's second wife (they would have to be at least partially siren, since his dad's wife is a half-blood siren).
The options are endless and I am happy to talk plotting if you have additional ideas. Other than his half sibling needing to have a half-blood Siren as a mother, Kaleb's sibling can be of any path and they do not need to be a shifter like him.
Lastly, sibling can be older or younger. I imagine him being older, but I am flexible.