Hwang Min's arrival
Their mansion is heavily guarded, and her cars are bulletproof. When she leaves the house, she is surrounded by numerous guards that even a sniper cannot penetrate. She doesn't go to crowded places, nor does she attend events without a top-notch protection protocol for life.
Her reason for being so careful is to protect herself from none other than her husband. Before going to bed, she'd make sure to send pictures of Brian to her husband as a goodnight message.
It's not because she wants her husband to see that their son is sleeping or doing fine, but to remind him that someone is watching him closely. If she doesn't wake up, Brian will be killed.
Hwang Min had killed and changed Brian's servants a couple of times. He had also changed Brian's rooms, but he was still getting those pictures every night.
To not risk killing his own son, Hwang Min aborted the thought of killing Nancy in her sleep.