Responses
Ch 96*
Im pretty sure it's not his actual sister but his cousin. He probaby called his cousin the chinese word for "sister" and so the translator decided to just translate it directly as sister.
Asian culture often refer to girls and boys that are relatively within the same generation as sister or brother as sign of closeness.
Same as with calling women and men in the older generation aunty or uncle no matter if they're actually one of their parents siblings or even actually related.
Reread this but I've never caught on to this plot hole where on the birthday episode of li huan, with his father said that on his birthdays theres only three of them in the family even on all the other flashbacks they are depicted as a family of three and then in ch 92 he suddenly has a sister