Hi Jill
Not sure if the marriage for Samuel and Agnes is there to be found unfortunately. From general searches, there are a number of people researching this family and none show either marriage details or parent details for Agnes.
From your original list of children showing for Samuel and Agnes, there are a few more showing on trees that you might want to follow up on:
1. Jane Wells
Birth: 1807 - Scotland
Death: Aug 1836 - Middlebie, Dumfries-Shire, Scotland
2. Ann Wells
Birth: Abt 1808 - Middlebie, Dumfries
3. Thomas Wells
Birth: Abt 1813 - Middlebie, Dumfries (Dumfries-shire)
Death: 28 Dec 1879 - Dumfriesshire, Scotland
Marriage: 19 Dec 1836 - Dumfries, Dumfries-Shire, Scotland
Spouse: Mary Gillison
From the 1851 census, Thomas above with sisters Margaret and Ann:
Thomas Wells 38, Master Shoemaker, b. Middlebie
Mary Wells 35, b. Glencairn, Dumfries
James Wells 11, b. Middlebie
Samuel W Wells 9, b. Torthorwald, Dumfries
Agnes P Wells 6, b. Torthorwald, Dumfries
Margaret Wells 4, b. Torthorwald, Dumfries
John Wells 1, b. Torthorwald, Dumfries
Ann Wells 43, sister, pauper, b. Middlebie
Margaret Wells 31, sister, pauper, b. Middlebie
Address: Dfs Road, Collin, Torthorwald
Sisters show as living with Thomas and wife up to at least the 1871 census.
With the above possible children, marriage for Samuel and Agnes pre 1807 - unless some of the earlier daughters were Margaret McNays?
Monica