Hi Abiam and Kirsty

Not sure if I am going to help, I think more likely raise more questions.
Abiam, from the details you show for Evelyn's parents:
I think I have the Marriage cert for her parents which shows:
John McClumpha McClelland (Ploughman and living at Barrhill or Barnhill) and Mary Stewart (20 and living at Knockdolian, Colmwell?) married 25 November 1890 in the parish of Girvan in the county of Ayr. But I notice a C before Lelland!
John is 21 and his father is William McClelland (another ploughman) and his mother is Mary McClumphaI think John was likely to be illegitimate. This looks a possible birth entry from IGI:
JOHN MCCLUMPHA Birth: 04 AUG 1869 Whithorn, Wigtown, Scotland
Parents: MARY MCCLUMPHA
From the marriage you have in Girvan in late 1890, I think this might be the family of John and Mary (Stewart) in 1901, with a corresponding birth place for John:
John McClelland 31, ploughman, b. Whithorn, Wigtown
Mary McClelland 30, b. Girvan
Elizabeth McClelland 9, b. Girvan
Mary McClelland 7, b. Girvan
William McClelland 4, b. Kirkoswald, Ayrshire
Isabella McClelland 2. b. Maybole, Ayrshire
Address: High Milton Cothouse, Maybole Ayrshire
A check on any of the children's birth certs above would let you confirm mother's maiden name/marriage date to make sure it is the right couple.
What was Evelyn's age at marriage?
Could the Isabella above, age 2 in 1901, have been one of the witnesses at the marriage in 1913?
And where was Evelyn in 1901?
Monica