Why not invited them in...? Mother VDS probably knows nothing and Daddy VDS was nervous (per Greta) during the interview. Besides inviting the Natalee's mother in with a camera right there would make people think just like you are thinking.
People who have something to hide are some of the best players in the world. Beside have heard of a poker face? I sure Daddy VDS knows how to put on a poker face real well.
You have to remember Daddy said no rolling cameras, if their were camera's you might feel differently after we all got to see him in front of the camera.
Did you see the shot of Paulus in the bushes at the beginning of the video? N's mom was calling out to him and eventually he came out.