Where can I find information about Robert Stevenson and his family?

Firstly, look at published histories: R L Stevenson, Records of a Family of Engineers (1896); B Bathurst, The Lighthouse Stevensons (Flamingo, 1998); J Leslie and R Paxton, Bright Lights: The Stevenson Family of Engineers 1752-1971 (1999); C. Mair, A Star for Seamen: the Stevenson Family of Engineers (J Murray, 1978).

If you need to consult original records, start at the National Library of Scotland, which holds the business records of Robert Stevenson and Sons (Acc. 10706).