Thanks again, this has cleared a lot up. The 1851 census is still a bit of a mystery, with the whereabouts of Alexander but at least we have confirmed George, William and Alexander are brothers and survived childhood, went on to marry and had families.
We have not confirmed Williams parents are Andrew and Isobel Brown but it does look that way.
I had found the death of William Cowie, Sailmaker, at sea in 1890 but suspected this was George and Janes son as George was a a Sailmaker on the 1841 census, I think you have confirmed this.