What a tangled web we weave.
Here is my shot at it and a recap of what you have found
On the 1861 Census John Roberts born 1826 is a Widow living at the North Side of High Street Conwy with:-
Trevor Roberts born 1849 Son
Mary " " 1852 Daughter
Alfred " " 1854 Son
Eleanor Owen " 1832 servant ( I think she could be a relative of his dead wife, possibly her sister). There are also Sarah, Thomas And John Owen who I think are Eleanor's children as her daughter Sarah and John's Daughter are both age 9.
When I looked for a Baptism for Trevor Roberts I found one in Conwy 14/4/1850, father John Roberts, Mother Anne, address Mount Pleasant, Conway. Also on the GRO it states his Mother's maiden name is Owens
Baptism for Alfred Roberts 16/4/1854 Conway same parents and address. GRO birth Mother Owens
Marriage for John Roberts & Anne Evans (she was a widow) 14/12/1847 at the Parish Church Conwy. His father was John Roberts, Occupation Mason and her father John Owens, Occupation Mariner. The witnesses were David Roberts & Elin Owens.
1851 Census Mount Pleasant Conwy.
John Roberts born Conway 1825
Anne Roberts " " 1822 Wife
John Evans " " 1841 Stepson
Evan Ellis Evans " " 1844 "
Trefor Roberts " " 1851 Son age 11 months (so he was born 1850)
Owen Owens " " 1822 Lodger ( possibly Anne's Brother)
Eleanor Owens " " 1828 Servant ( possibly Ann's Sister)
Anne must have died sometime between 1851 & 1861 as John is a widower on the 1861 Census
There are Monumental Inscription booklets in Conwy Library both for St Mary's graveyard and St Agnes Cemetery with quite a lot of information. I will carry on looking to see what I can find.