One brother, Armand, had remained with their father, while the other, Joseph, arrives with his much younger fiancée, having been fired from his job. Happy he isn't. The third sibling, their sister Angèle, is a successful actor who left the villa some 20 years earlier after a traumatic incident and has not previously returned.
It is winter in the small coastal town and port in the Marseilles area and the family's small restaurant isn't busy. Bérangère, Joseph's fiancée, has grown tired of him since he lost his job and is eyeing up a young doctor, the son of elderly neighbours. Angèle really doesn't want to be there at all, but receives unexpected adulation from a young fisherman, Benjamin, who has adored her ever since seeing her perform when he was a lad.
As time passes Joseph accepts that he must let Bérangère go, while Angèle eventually lowers her defences in the face of unrelenting attention from Benjamin despite, as she says, being three times old enough to be his mother.
And then something happens that brings them even closer together.
On IMDB, a reviewer complains that this film has no story and no structure, but that's entirely missing the point. This is real life, not movie fantasy, and as such it is very authentic.
The Hollywood Reporter offers a far more informed review, which answered my question as to how the sequence was obtained featuring these people as their younger selves. You will see what are clearly the same people and this isn't the sort of film that would use CGI trickery.
In summary, it's very French !