Christina marries William Stewart July 11, 1862. He is 26 and she is 21. He is a saw miller and she is a domestic servant.
1871 Census living at 14 Rose Street, Dundee
William Stewart, age 34, wood sawyer
Christina Duncan Stewart age 35
1. William Stewart, Jr 10 (illegitimate)
2. Charles Stewart, age 7
3. Robert Stewart, b 1866 age 4 When the boys were born they lived on Fish Street, Dundee.
4. George Duncan Stewart, born 1866, age 4
5. David, Pirie Stewart, age 3 mo (born 9 December 1870) FHL number 6035516
1881 census: They are living at 143 Nethergate, Dundee
Christina Stewart, washerwoman age 40 born 1841
(Husband William deceased four years ago.)
1. (William Stewart gone from home)
2. Charles Stewart, apprentice baker, age 17, born 1864
3. Robert Stewart apprentice tailor, age 14 born 1867
4. George Duncan Stewart, message boy, age 14 born 1867 (birth GS number 6035516, parents are William Stewart and Christina Duncan)
5. David Pirie Stewart not in census, deceased
6. Annie Stewart, Scholar age 8 born 1873, Falkirk, Stirlingshire
It was a 15 minute walk from 11 Crescent Street where Margaret Stewart lived with her father Robert Stewart to 8 Fish Street. Margaret could then see her twin nephews. I'm sure her father Robert accompanied her to see his grandchildren. 
Fish Street, Dundee - Ref: WC0174
This area was demolished in 1878 to make way for Whitehall Crescent. The spire of St Pauls Cathedral can be seen in the distance. At one time Fish Street was occupied by respectable well-to-do tenants.
By the middle of the 19th Century Fish Street had lost its appeal with the merchants and middle classes and became occupied and frequented by unsavoury characters. It was the referred to sarcastically as "The Holy Land"
The following is for reference only. Apparently our Robert didn't marry Agnes Stewart because on their marriage certificate it says his mother was named Catherine not Christina.
1901 Scotland census:
Robert married Agnes Anderson in 1890.
Grangemouth today:
Grangemouth is a town in east Stirlingshire and is part of the Falkirk council area, Scotland. The town lies in the Forth Valley, on the banks of the Firth of Forth, 3 miles (4.8 km) east of Falkirk, 5 miles (8.0 km) west of Bo'ness and 13 miles (20.9 km) south-east of Stirling. Grangemouth had a resident population of 17,906 according to the 2001 Census.[2] Preliminary figures from the 2011 census reported the number as 17,373.
Grangemouth's original growth as a town relied mainly on its geographical location. Originally a bustling port, trade flowed through the town with the construction of the Forth and Clyde Canal in the 18th century. Nowadays, the economy of Grangemouth is focused primarily on the large petrochemical industry of the area which includes the oil refinery, owned by Ineos, one of the largest of its kind in Europe. The town is twinned with La Porte, Indiana.[3]
Residents of the town are known as Portonians.
Bridge Street, Grangemouth:
Arial view of Bridge Street today:
Research:
Brechin is very close to Dundee.
