The real enemy is that mother. Selfish, she's afraid of destroying her social image.

Rather than social image i think she is afraid of losing her concept of family that is why even when seo-in told his adopted mother that his brother has been bullying him the mother instead choose to protect the whole harmonious family make believe she wanted

Also, remember what place she has within the family. Remember how the public criticized her mother...

Oh shit, the father is worse, right? I mean, he doesn't even show up, hahahahaha