Complex sentence: The father is haunted by the memory of Marguerite, his great love of youth, and lives only in the hope of finding her, while the son, somewhat lost in his life, later taking the measure of his attachment to his grandfather.
Split into simpler sentences: The father is haunted by the memory of Marguerite, the great love of his youth, and he lives only in the hope of finding her. The son however is somewhat lost in his life, and later takes the measure of his attachment to his grandfather.