Long story short: There not real brothers okay the Hyung nim is not blood related and just adopted. Both was saw by the father having sex so the Hyung nim kill the younger brothers real parent and then take over the family and keep the young brother Dongwin lock to the house even the older one is married he keeps the younger brother for him self because his so obsessed and love the younger one the the younger one didn't run away and stayed with him after all.
Long story short: There not real brothers okay the Hyung nim is not blood related and just adopted. Both was saw by the father having sex so the Hyung nim kill the younger brothers real parent and then take over the family and keep the young brother Dongwin lock to the house even the older one is married he keeps the younger brother for him self because his so obsessed and love the younger one the the younger one didn't run away and stayed with him after all.