Hello again
This is very strange. There is no sign of Janet, b. circa 1851 on the 1861 - either as Janet, Jessie, Jean or Jane with either Shackleton or Grieve (variations) as a surname in either Roxburgh or Selkirk.
What I have found, and it's the nearest to a family yet, is this:
Death 27 July 1866, Lilliesleaf:
Robert Grieve, farm servant, aged 37. Illegitimate. Married to Jessie Patterson.
Parents - Robert Scott, Ag Lab (reputed father) and Margaret Rankin, m.s Grieve (deceased)
I then found this marriage:
Robert Grieve and Jessie Patterson 12 Feb 1853, Lilliesleaf
Children of this couple on IGI:
3 July 1853 - Mary (mother as Margaret - I believe in error see below)
18 Oct 1855 - Margaret
29 May 1857 - William
15 March 1859 - Helen
17 Feb 1861 - William
and:
1861:
Easter Middles, Lilliesleaf
795 ED 3
Robert Grieve, 31, ploughman
Jessie, 27,
Mary, 7
Margaret, 5,
Ellen, 2,
William, 1 month
all b. Lilliesleaf
Gadget