So from what I got is that
Both twins lived together alone without parents & since the sister is the oldest she had to take care of he brother right! so even tho she didn't like raising him because she'll not be living her life the way she wanted it, despite that she raised him so, she thinks that the brother is obliged to tell her everything, so when he didn't she then went and spied on him then she saw this Lui guy, so she was furious that he didn't tell her about him, basically she's a brocon! although they didn't mention it it's looks like the sister knows that her brother is gay, so, so far it looks like the sister dating her brothers' love interest is out of revenge but I hope she's a good one
For Lui and Yiyi it's looks like they dated before and Yiyi cheated on him so they broke up then Lui fell in love with Zinon and forgot about Yiyi and Yiyi still likes him you know typicall third wheel drama
No, yiyi never met him in my eyes, in the first place it was a random pick. Yiyi didn't pick him because she has known him (which isn't the case), it's because she cares about him & maybe who knows? Maybe she knew him but I don't think there is any relationship related from yiyi to zinan. Yiyi could've thought that he was good looking & send him out to Liu because she thought that it might be IT, yk? Zinan's sister might be a bit weird but uhm everyone has their own problems..., Right? Anyways it could be true but that would be kind of strange..., I don't see yiyi as someone to set something up for someone who doesn't even want to? I guess zinan wanted something exciting to test his sexuality..anyways maybe you're right, nothing is impossible in this world here.
I’m just so damn confused