In her January Bazar interview, she mentioned about her mom and older sister. So yeah she does have a sister at least. And I think I've scrolled down RHY's Tumblr tag before and saw someone posting that her sister is a rookie actress too?
About her family's view of her and GKP, yeah I'm curious about that too. I think someone briefly translated the interview before, where she mentioned about er mom in real life texted her something like, "you've kissed with GKP already?" lol. If I were her family I would ship them so much haha but then they must know her well enough to know that if GKP is really her type or not.
On a different note, I read an interview of the actor who plays Noeul before. He said that the PD casted actors not based on how well they act, but how similar the characters are to to them in real life. So I was wondering, how similar is GKP tp Sunwoo lol. I'm sure he's not extremely nice like that, but I wonder to what extent he is. And also, I remember in their interview, RHY said they were both very mischievous as friends, but she also mentioned that GKP was the handsome and nice at the same time kind of sunbae so he was popular in college haha