That's the thing i find a bit annoying to be quite honest. The sister is none the wiaer, i would have, as his brother (the seme) told the sister about it before exposing the trash. Then again, we don't know what the sibling dynamic is between them
You know tho? The sister clearly was with someone while she was suggesting what to do with the company to her fiance, I guess her brother told her to do it and what to say, after he'd shown her what human case she was getting married to
Is he going to display the video to everyone at the wedding? Is really necessary to humiliate her sister?