....I cannot find James Bertram Sim on the 1901 ....
Possibility that James may have been out of Scotland (also possibly GB) given his occupation on the marriage cert that lindy-lou transcribed which showed James' in the 1st Battalion Gordon Highlanders. Second Boer War years were 1899-1902 for one.
Norma, agree with your summary

Just found some A/try family trees for this Sim line. Nobody else has been able to find that 1861 census entry for the family either!
Monica