The two restaurants facing each other were digitally created: the house which was presented as Maison Mumbai actually faced a large field. They paved a 75 m stretch of road and a building facade on the opposite side with a blue screen on the top. (More details on the fxguide dot com website of the film.)
The upscale restaurant in Paris is actually Georges at the top of the Pompidou Centre although renamed in the movie apparently as a fictional restaurant.... But it was a set
The EU (formerly EEC) was formed in 1957. Britain (from where the family moved to France) joined in 1973. Hassan appears no older than 30 at the end of the movie, therefore the depiction of the family's move to France from London would have been between roughly 1990-95. Mobile phones were common at the time.
Marguerite collected mushroom called Boletus luridiformis which is fully edible, but she was told by Madame Mallory that it is Boletus satanas which is poisonous.