Well found, ev!
Clearly, KayeG, you have further information which would have helped us initially - first, neither of the 2 girls were born in 1870's!
Susan Boyd Simpson b.14/1/1869 Edinburgh, dau. of Marion Simpson (as posted by ev).
Jessie Margaret Maxwell Simpson b.19/12/1862 Dalkeith, dau. of Marion Simpson (both are on familysearch).
In 1871 - Jessie with with her grandparents John and Agnes Simpson in Dalkeith
Susan is with her uncle/aunt, Robert and Margaret Simpson in Dalkeith.
John Simpson born 8/10/1807, bp.25/10/1807 Pencaitland, East Lothian (birthplace concurs with census), son of Robert Simpson and Marion Malcolm.
John Simpson (a joiner) married to (1) Margaret Thom(p)son although I haven't been able to find the marriage. 1841 census shows them with children, Margaret 12, Robert 10, John 8, Mary J. 5, James 3 and twins Marion and Jemima aged 2 months.
Found some of the baptisms on familysearch - if you look them up you will see full dates:
Robert 1828 Newbattle (ties in with census birthplace)
John 1833 Newbattle
Marion McAdam )1841
Jemima Thomson )Dalkeith
William 1844 Dalkeith
Alexander 1847 Dalkeith
By 1851 John appears to be a widower and remarried (2) to Agnes Tully, widow, on 29/12/1859 Dalkeith.
Jessie's birth certificate gives no indication of who her father is - however, with Maxwell in her given names it would suggest this was her fathers surname.
Hope this helps but please give as much info. as you can in any future posts.
Annette