This chapter is confusing.
When the delinquent grabbed the maid's arm, the delinquent said, "WHO ARE YOU?"
And then the subsequent dialogues definitely implied that they are strangers.
But when the maid catched the delinquent's kick, the maid said, "But I think you still recognize me as YOUR OLDER SISTER..."
Maybe that "older sister" is just the translation of "unnie" which does not definitely imply that they are blood sisters as in many asian languages.
But then the delinquent said, "Has she become more powerful than OUR dad?"
So which one is it? Are they actually sisters or the translators made a mistake?