updated August 2010
William Montague Graham was the eldest son of William Graham, a soldier from Scotland serving in the HEIC army, and his second wife, Eliza Montague.
I calculated William Montague's year of birth from his father's estate administration where he is said to be "an infant of eighteen years or thereabouts".
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 Montague Graham married Lilly Staig in Trivandrum on 24 July 1862 and they had at least five children. I found William and Lilly's marriage record in the registrar's records at the British Library, this gives William's occupation as "Overseer A.V.M. Canal" and the names and occupations of both the Bride and Groom's fathers. One of the witnesses at the wedding was A.H. Shedden.
According to a Wikipedia, the Anantha Victoria Marthanda Varma Canal (known as the A.V.M canal) was formed in 1862 during the reign of Marthanda Varma, Maharaja of Travencore state.