How could Du You possibly be oblivious to his own followers? Although Du You never explicitly asked, he was stealthily observing them through some surveillance equipment at home.
Observing what goes on in his own home is hardly an intrusion, Du You thought.
Actually, every villa came equipped with such surveillance devices, but its functionalities were limited. For example, it wasn't installed in more private places like bedrooms and bathrooms.
Du You was not a pervert who would voyeuristically spy on these areas. They were his loyal followers; if he really needed something, he could directly confront them, so there was no need for snooping, Du You thought with smugness.
Through observation, Du You gained some understanding of the sisters, Lin Yucha and Lin Yushi.
As it turned out, the old man really was their biological father, and their mother was not as old. These situations with huge age gaps between husbands and wives were quite common in this world, nothing too unusual.
