father keeping his daughter n his so called grandchildren underground

A father raped his daughter since she was 14 years old. He had kept her underground since he had done that to her. She gave birth to a total of 4 children,3 girls and 1 boy. they were all born underground. Instead of calling their mum's dad Grandpa,they call him dad. He had hidden them underground which is linked from his house. His existing wife who gave birth to the girl who was raped, believed that the daughter had ran away from the house with her boyfriend. The old man writes letter and drops them at his own letter box, pretending that the letter was written by his daughter and passes them to his wife.
The old man was caught when he had no choice but bring his daughter whom he raped to the clinic together with the child he had with her. She told the doctor just to save herself an d her children.