Complex sentence: With the option of returning to Norway to live with relatives, Dahl's mother decided to remain in Wales, because Harald had wished to have their children educated in British schools, which he considered the world's best.
Split into simpler sentences: With the option of returning to Norway to live with relatives, Dahl's mother decided to remain in Wales. Her husband Harald had wanted their children to be educated in British schools, which he considered the world's best.