Complex sentence: He was the youngest child of six and had much older brothers (and an elder sister); two of his brothers were killed in the Second World War, one as a Spitfire pilot and the other as a rear-gunner in a Lancaster.
Split into simpler sentences: He was the youngest child of six and had much older brothers and an elder sister. Two of his brothers were killed in the Second World War, one as a Spitfire pilot and the other as a rear-gunner in a Lancaster.