Thanks everyone for all the work while I was asleep!
Tom - I would never had thought of looking at The Scotsman archives, and yet there is an obituary notice for Christian Kent. Like many of my family members I am named after her, so I guess I have a special interest in finding out more about her.
Andrew Smith Sr is definitely Andrew Smith Jr's father, and it is his will and death notice in 1857. I originally thought I had Andrew Jr's death notice too, until I noticed the age (which agreed very well with the birth date I already had for him). So more family history filled in but not the elusive Andrew Sr.
Monica - I am related to Andrew Smith Jr Jr who ends up in Peebles, and our family has quite a bit to go on with working out things from him on (including photos of his wife Helen, although not of him alas). I too am confused by the marriage certificate, that notates John Bertram to be deceased, but not Christian Smith, who most definitely is dead by that stage. So it seems to be an unreliable source of information for once, which is strange for a family of accountants and watchmakers not to be totally meticulous!
The Jane Smith link is maybe promising - two of her brothers seem to be in Edinburgh at the same time too. Trouble is unless she uses her more unusual middle name (which she never seems to again) it is so hard to verify a Jane Smith! Thomas Swanston and Charles Kent seem to literally use their middle names as part of their family name for the rest of their lives, which makes tracking them down much easier...
That being said the findagrave reference is magnificent thanks - it filled in lots of details about Thomas Swanston and his family. I never expected to see that - my searching is obviously not up to scratch! Even now I am not sure how you found it!
So thanks again - still not closer to finding Andrew Smith Jr, but lots of useful things to me so far. I am very grateful for everyones time and energy.