I think the answer is to avoid being too specific, and just give a brief picture, or else it would take hundreds of words to even begin. Erik Orsenna' L'Exposition coloniale was the Goncourt winner for 1988, and is a breathless read which includes most of the protagonist Gabriel Orsenna's life, and before he was born. No, it's nothing to do with Orsenna's family, its fictitious, and in any case Erik Orsenna is a pseudonym of Éric Arnoult.
Marguerite is the grandmother who had a very brief liaison with a Mexican who swiftly dies, although the result of that is that Gabriel's father Louis is born. Louis is a much-married man who was originally a book seller (specialising in travel), and as he has few opportunities for sex elsewhere, Gabriel is conceived during a quick one when the shop is empty.
Gabriel doesn't take after his father in the sex stakes, and differs from Louis in a number of ways. Louis appears in the book episodically, even in the form of an imaginary letter at the end: this book is in part one of dreams and imagination. Ever since he was a young man, Gabriel has dreamed of the Knight sisters from when they were pre-adolescents, and when they are old enough he finds it difficult to choose between Ann or Clara. Ann later becomes a business woman, and the rather disturbed Clara is to have a brief intellectual flirtation with Freud, and then settles into taking photos of everything.
Before that, though, she marries Gabriel. Gabriel is into Auguste Compte's positivism, and also (non-sexually) into rubber: he's an expert on the subject. On his honeymoon the couple take the boat for Brazil, where Gabriel is to work on the rubber plantation. But the flighty Clara leaves him where he is as soon as they land, and Gabriel becomes catatonic in his distress for three months. Interestingly, what pulls him out of it is words from a book one of the bosses from the rubber plant gives him: the only other book of Orsenna's I've read is about the power of language: La Grammaire est une chanson douce (2001), translated as Grammar is a Gentle, Sweet Song.
Clara doesn't leave Gabriel completely, and nor does Ann, and although they remain with him only briefly, and although sex between them is very infrequent, Gabriel doesn't listen to his father's advice and continues to put up with their capricious behaviour. All through his dealings with the rubber business, which takes him to many places: L'Exposition coloniale is a mad romp through the world, the characters often larger than life, and frequently very humorous.