Can't figure this out (origin of the fake Cellini)
Ok, I've only seen this film once, and I may have missed some points so bear with me.
From what I gather, the Bonnet family has the true works of art stashed in the secret attic, and all the works that are sold/exhibited are the forgeries. Ok, so this implies that the true Cellini is somewhere in the attic.
Why then did Nicole's grandmother have to pose for the forgery? Couldn't the grandfather just copy it directly from the original as Papa does? I know the plot required the grandmother's posing so that we could see the likeness between the statue and Nicole. But logically I can't make sense of it.