Keep reading broh. They r not twins, they just happen to have very similar face.
answer
yes the mistress is the blue hair one but she wear wig
Answer:
If you read the manga it shows they aren't twins, Yoosun is just a girl that looked like the mistress (also the flower maiden) and they change places when the mistress goes through her blooming period. You can tell by the earrings, when Yoosun is the mistress she wears red earrings and when mistress is mistress they are blue.
wait idk understand.
spoiler
there is this royal family and they had twins
one of the twins is mstress while the other is her personal guard
the guard has a girlfriend or something that has blue hair and is a flower maiden. Is the blue hair girl also the Head mistress?