Just looking at Margaret Telfer
She seems to be listed having many illegitimate births. I don't know if these are all her but the end one says Quadrelapse which means she is a 'regular fornicator'.
1796 David Smith Tenant Cote Eskdailemuir
1807 William Elliot Jnr Broomieknow
1812 William Graham Claygate
1815 John Armstrong alias Grahm
1817 Joh Grieve now deceased & Margaret Telfer Quadrelapse
1820 David Alan of Barnliesh.
It certainly looks like a very long 'career'.
I wonder about the 11-year gap between David Smith and William Elliot, and that makes me speculate that perhaps there are two different Margaret Telfers in that list? Suppose that she was 16 when David Smith's child was born, then she would have been born around 1780, and aged about 40 by 1820, which seems slightly suspect, even if not impossible?
In the MIs for Canonbie church graveyard there is an entry that relates to Margaret Telford spouse of James Clapperton who died at Ladyhousestead 7th April 1867 aged 72 years.
So if her age is accurate she would have been born 1794/1795 and could not possibly have been the mother of David Smith's child in 1796, and aged just 11 or 12 when William Elliot's child was conceived. Also, she was married before your Margaret's quadrelapse. So I think she can safely be eliminated from your enquiries.
So how many Margaret Telfers were there?
By looking at the 1851 Census I see there is a Margaret Telford aged 74 at the top of the sheet. I haven't got the preceding sheet to see who else is on there.
The household is
William Anderson/head/mar/42/Langholm
Margaret Anderson/wife/mar/36/Canonbie
John Anderson/son/14/Canonbie
Margaret Anderson/daughter/10/Canonbie
Margaret Tilford/mother-in-law/wid/74/pauper/Canonbie.
John George Anderson, baptised 3 July 1836, son of William Anderson and Telfer (no given name)
Margaret Anderson, baptised 26 September 1841, parents William A and Margaret Telfer.
So on the face of it this Margaret T*lford is probably Margaret Beattie, who married John Telfer in 1803 and had four recorded children in Canonbie, including a Margaret in 1815. In which case she isn't your Margaret Telfer. If you do want to investigate her further, just in case, you should ask Dumfries and Galloway Archives
https://www.dumgal.gov.uk/article/15308/Local-archives if they have the Canonbie Parochial Board records and if so whether or not they mention Margaret T*lford.