Deb & Gadget.
Does this site award medals? If so, you two will definitely receive my nomination for your assistance above and beyond what ever could be expected.
The information about Nicholas being in America came from the 1881 British Census (The Mormon Disk set). there are two possibilities on the 1880 American census (On Familysearch.org)
in 1891 Nicholas & Ann are with their daughter Sarah J. in Lasswade. The 1891 & 1881 census states she is English however the information you have found on the 1871 census must mean this is the same family.
Of their siblings, William & Mary Ann made it from Cornwall to Scotland. Sarah (1861) does not appear to have made it to 1871, another Sarah J. (1870) has been born, either in England or Wales and survived as far as the 1891 census. Finally Susan was born in 1873 but died in 1878.
Bessy (1863) in new to me.
I will try and delve a bit further. I presume the information you have available is through subscription sites?, if so what is the best one to look at. In Scotland the information is all available through the government assisted site Scotlandspeople .gov.uk
Again thanks for the assists, any further pointers would be most welcome.
Bry