George William, your husbands grandfather, was born 1893 and died 1966, and married Rhoda Fitchett 1920 Derby which, of course, you must know.
Thomas Bostock Smith married Annie Loxley in 1911 at the Register Office, Derby and, as you say, he was killed WW1. Widow Annie married a Walter F. Goodwin in June quarter 1920 Derby. According to 2 sources her birthdate was 10/7/1892 and she died Dec.1971 Derby.
Francis H E Smith b.28/8/1894 married Elizabeth Fitchett b.8/12/1885 (older sister of Rhoda Fitchett) in 1917. Looks like they had at least one son Francis R b.31/7/1917.
Charles Millard Smith b.18/7/1897 appears to have married a widow Florence Jeffery in 1918. Her husband Thomas William Jeffery killed 1917 WW1. Florence's maiden name was Loxley and she was an older sister of Annie Loxley).
So, we have a case here of 2 brothers marrying 2 sisters times two! Which makes it, when working with surname Smith, difficult to identify which births belonged to which couple.
Annette