updated May 2010
William Staig Graham was the eldest son of William Montague Graham and grandson of William Graham, a soldier from Scotland serving in the HEIC army, and his second wife, Eliza Montague.
The information I have about this branch of the family has come from another researcher who is a descendant of William Montague Graham and from the updated births, marriages and deaths records on the LDS FamilySearch website.
William Staig Graham married Florence Arnold in Bangalore in 1887, they had at least five children. Two of these children, Ethel and Muriel have the same dates of birth, so I suppose they must have been twins or there is an error in the LDS FamilySearch data.
I have not been able to discover William's occupation, in the mid 19th century it was common for sons of soldiers to enlist in the "native" army and marry the daughter of another soldier. A search of the ecclesiastic records at the British Library might reveal some more information about William and his wife.