So the before secret, helped Ben, Sonja, Julien and Anaïs to credibile their secret. Sonja and Julien are in the same house, Anaïs and Ben are in the same house.
Sonja and Ben are the parents.
Julien and Anaïs are the children.
They decided that Sonja and Ben met in an elevator which was stuck. That they lived in Paris, they are Belgium of origin, they decided to live in Marseille after that Sonja went for her job.
(All is fake of course lol).