Complex sentence: Max had retired in 1973, but Jane continued working until 1979, when they both lived at their country retreat "The Lake House", at Rowfant near Crawley in Sussex, where they had often socialised with friends and family.
Split into simpler sentences: Max had retired in 1973, but Jane continued working until 1979. They already had a country'retreat' called "The Lake House", at Rowfant near Crawley in Sussex, where they often spent leisure time with friends and family.