Only one of them does
Which one?
The younger one, black hair, Jigu.
Do you remember which chapter is it?
No But I do remember the scene. Jigu started to get a suspicion when Yeowoon told him about the madeleines. Ch 57 basically summarized how Jigu figured it out - since that chapter and the next were told from his perspective.
I only skim it for now, but they still don’t know about each other’s real identity?