Juda's mom underwent surgery and was operated by Dohwa's dad (as I remember) but there was a mistake so they covered it up as failure. Hence, Juda's mom died. That's when she started living in Dohwa's family's house. Then she got kidnapped because they thought she was their child. Then, as we all know, it has caused a major trauma in Juda's life. Then, her grandmother thought something was weird with her daughter's death and wanted to know what really happened. To avoid letting our their secret, they killed the grandma to silence her by saying the surgery failed. I think that hospital is theirs so they are prominent in that field. Letting everyone know their failure would take a huge toll in their credibility and business. They're will be soiled.