I also believe the children have at least some knowledge of what happened to their mother.
Yes I want to just confirm I don’t blame the children in any way - I think they were witnesses to at least the aftermath of their mother’s disappearance and that York used that knowledge to manipulate them and threaten them. Maybe to intimidate them by telling them they will be deported for not reporting it when it happened, or maybe even menacing them into believing what he did to her, he could do to them too. Remember, York basically got away with whatever he did to his wife! She was gone for over a year with no law enforcement even looking for her!!! It took the good people of Websleuths to even put her name out there.
The children must have been so frightened and hopeless. York manipulated and bullied them every step of the way. I hope the PI is wrong about him being released.