Juheon's mom married against her family then died I think both of his parents then her sis adopted him for family inheritance
Juheon mom left her father and married someone and that someone turned out to be abusive so when abuse got too much she reached out to her sister for help but she didn't come through at that time which is why juheon's mom left the house leaving juheon alone with his dad. I don't exactly remember what happened to juheon's father.
But then the aunt came to "adopt" juheon because she wanted the inheritance and basically be recognised by her father. She emotionally abused juheon by manipulating and using juheon's feelings. She even hid the fact that juheon's mom was dead and used it to her advantage.
I know dohu and gitae issue is bullying but I seem to forgot what is the issue of juheon to his family (￣∇￣")