Ok, I've had a chance to digest the info given by ev and Steve....
First, ev, thanks for the 1881 & 1891 census info.... I agree everything fits so it really has to be them in both cases. I didn't previously know about John F Christie or Florence so they are totally new people in my family tree. Did you got this info from Ancestry.co.uk?
Also ev, when you say "The 1861 census is something else" what do you mean? I think it looks possible to be the same family as James (the son) is 2 years of age which would mean he could have been born in 1858 and not yet turned 3 when the census was done. Also, from the marriage certificate of James Christie and Barbara Finlayson in 1878, it shows his mother's maiden name to indeed be "Fettes" so I think it is most likely to be the same family. If you don't think it's the same family what makes you think that? (i.e: what have I missed?!)
Sorry if I confused you re Barbara Christie... there are so many James Christie's it's hard to explain it all clearly. Anyway, there was only one Barbara (nee Finlayson - note, no 'd' in the name, despite the census adding one) who was married to James, my great grandfather (and yes, she died in 1932 in Arbroath). From the same marriage certificate I can confirm that Barbara's parents were John Finlayson and Mary Mitchell.
If you look at the link I posted to my g.g.f James Christie's birth cert in my first post you will see his mother is listed as Matilda Mahon and the father is also James Christie (therefore my great great grandfather). It is this man I suspected was in fact already married (to Mary Fettes it would now seem) with children and obviously had a fling with our Miss Mahon who most likely worked at the same mill.
So I guess now I can do a search on ScotlandsPeople or the IGI etc for a James Christie born around 1817... am assuming it was in Arbroath since but naturally he could have come from anywhere.
Thanks also for the 1891 census info... I am guessing the person doing the census simply assumed the Finlaysons name had a 'd' in it - interesting to note that the two Christie grandsons lived with them.... Very interesting that neither James, Brabara or George Christie are in it. I can't help wondering if they went out to NZ or somewhere else to build a new life leaving the two youngest sons with their grandparents until they could afford to send for them. Although given they both died in Arbroath I guess that seems unlikely... perhaps they were just so poor they needed help to clothe, house and feed the 2 younger sons James and John. Or perhaps Barbara was ill or just not a good mother, hence my g.g.f divorcing her around 1909.
All questions which I doubt I'll ever get a definitive answer to.
Another Q - for people like this who were very obviously working class and probably very poor would they have been likely to have had headstones when they died? If so, does anyone know any way of finding where they might be buried? (I guess I'd need to write to Angus Council for that info as I've not found it online anywhere.)
Thanks also for the two websites - I had previosuly stumbled across them and
http://www.arbroathtimeline.moonfruit.com/ is very, very useful (shame about the annoying music but you can't have everything!). The Angus council site I will keep my eye on as it appears so far not much is available online.... later this year there will be more according to them.
The problem with doing this is i could ask a million questions... but I'd be here night and end up doing a Tolstoy!
Many thanks again for the help.... it's allowed me to make a lot of headway in just one day!
Mike