I don’t have any connection to the Douch family, as far as I’m aware, but thought I’d help with a little research. The Commonwealth War Graves Commission website records that William Henry Douch was 29 when he died on 31 July 1917 and was the son of Lydia Elizabeth Douch of School Hill, Burwash.
William Henry Douch appears to have been born in early 1888 in Burwash, and was the son of Edward Douch (born Mayfield 1853) and Lydia Elizabeth Jenner (born Burwash 1861) who married in 1881. At the 1901 census they were living at School Hill and there were 6 children in the family – Annie, Edward, William, Charles, Ellen and Kate. I believe there was also a further son George born in late 1901
I hope this will help in tracing a Douch family member.