It is suggested on the wiki that he looks like Dillin Derito from the Malpractice household: https://sims.fandom.com/wiki/Dillin_Derito
The lore is my favourite part of the sims games but unfortunately what you've found about this vampire sim might be all there is.
As for what you said about the affiliation between this vampire and Inna needing to be recent, while the modern decoration in Lilith's bedroom in the gameplay trailer (https://www.youtube.com/watch?v=3qx2qMYhgp8) may suggest Caleb and Lilith were recently turned, this doesn't seem to be canon. In the Werewolves gameplay, the dialogue you can get with Lily Zhu suggests that the trailer is innacurate about the timeline (though not about everything) and that Caleb and Lilith were turned into vampires earlier than the trailers would suggest.
If I find more lore about this vampire sim though, I'll be delighted!
