One lead is that on 1881 census (as Robson) John states he was bc.1853 Spittal, Berwickshire and
Elizabeth bc.1854 Coldstream, Berwickshire.
Also on the 1881 census is James Pearson, lodger who was probably Elizabeth's brother.
He also gives his birthplace as Coldstream, Berwickshire
On the 1911 census, Elizabeth Robertson, widow states she has been married 32 years.
This put the marriage at approx 1879
Sorry no luck finding the elusive marriage for Elizabeth Pearson to John Robertson/Robson

There is this
1861 census with a brother and sister together , all
born Coldstreammaybe a possibility for Elizabeth Robertson nee Pearson

Address: 28 Duke Street Coldstream Berwickshire
John PEARSON 42 occ.
Shoemaker JourneymanCatherine Pearson 36
John Pearson 14
Margaret Pearson 12
George Pearson 10
Robert Pearson 8
Elisabeth Pearson 6
James Pearson 4Andrew Pearson 7 Mo
Betty RICHARDSON 80 mother
This appears to be Elizabeth Pearson on 1871 census
1871 census Address: 30 Duke Street Coldstream Berwickshire
Elizabeth Pearson age 16, Coldsm, berwick, Boarder Occupation: Servant Domc
Sinclair Knox 67
Catherine Brown 68
And in 1871 James with his mother and one sibling
1871 census. Address: 24 Duke Street Coldstream Berkshire
Catherine PEARSON Head age 46, Coldstream berwick
Occupation:
Shoemakers widow Under Washerwoman
James Pearson 14Andrew Pearson 10
1851 census Address: East Market Place Coldstream Berwickshire
John PEARSON Head, age 32 Coldm, Berwickshire Occupation:
Shoe MakerCatherine Pearson 24
John Pearson 7
Margaret Pearson 5
George Pearson 3
Elizabeth Pearson 70 Mother
1841 census address: Coldstream Duke Street
John PEARSON age 20 Berwickshire, Scotland. Occupation:
Shoem ApElizabeth Richardson Age 55 occ Ag Lab.