The 1845 marriage and the 1855 Census record appear to be wrong they are different people. Your Manx link, if there is one, must be much further back. I managed to locate census records for your grandfather Edward from 1900 to 1940. Then I looked at your great grandfather James on census records for 1900 and 1910. There was a difference in his birth place one saying North Carolina, one saying Georgia. There is a match for Georgia that I think is right and I think the family line goes back there. I wasn’t able to locate census records for 1860, 1870, 1880 or 1890 but the births of children show the movements of the family.

Edward Watterson bc1887 (Texas or Alabama?) to 1963 (California)

1940

familysearch.org/ark:/61903/1:1:K96F-VVS

1930

familysearch.org/ark:/61903/1:1:XCJX-7DC

1920

familysearch.org/ark:/61903/1:1:MH71-HBF

1910

familysearch.org/ark:/61903/1:1:MLQN-L1H

1900

familysearch.org/ark:/61903/1:1:MSRP-ZN7

.....................................................

James Watterson bc1840s (North Carolina or Georgia ?)

1910

familysearch.org/ark:/61903/1:1:MLQN-L1W

1900

familysearch.org/ark:/61903/1:1:MSRP-ZN9

This 1850 Census record could be James it shows him aged 6 (bc1844 in Georgia) living in Roswell, Cobb, Georgia with what looks like his mother called Mary and various siblings all born in Georgia, no father recorded:-

1850

familysearch.org/ark:/61903/1:1:MZYK-W65

.....................................................

I think this is James getting married to Charlotte Elizabeth Mills in Alabama in 1870:-

familysearch.org/ark:/61903/1:1:QKZS-FX7D