That was my first thought as well. I only know of him having three brothers, one of which I know wasn’t dead yet. So either he had a brother I didn’t know about, or for the sake of avoiding a desertion conviction was fantasizing the story. Although certainly he didn’t mean three brothers died at once. I know one of his younger brothers died at 10 years old, so perhaps he meant three brothers up to that point as he does finish the letter stating he is the only son left…etc. thank you for your help!