Chen Ge's initial plan was to find Ying Tong, but from the clues that he had found so far, the plan might need to change. He probably needed to locate all four children: Ah Ying, Ah Mu, Ah Tong, and Ying Tong.
"Ying Chen should know about the existence of the three brothers. In fact, one could say that the existence of the three brothers is deeply linked to him. He alone created this tragedy. The three children each suffer from a different type of mental illness, and it is most likely Ying Chen who caused this to happen. They correspond to respectively the fear of sharp objects, imprisonment in a small room, and being scared.