The youngest brother Robert Lawrie married Elizabeth Brown in January,1869.
Name Robert Lawrie
Spouse: Elizabeth Brown
Marriage: 6th January, 1869, Edinburgh Parish, Edinburgh
Their bairn Robert Brown Lawrie was born the same year.
Name: Robert Brown Lawrie
Birth: 6th October, 1869, EDINBURGH PARISH, EDINBURGH
Father: Robert Lawrie
Mother: Elizabeth Brown
I cannot find a death or a census return for young Robert B. Lawrie.
1871 census: Wrights Houses, 16, St Cuthbert Edinburgh
Robert T Lawrie Head 25 1846 Foreman Baker Midlothian
Elizabeth Lawrie Wife 25 1846 Midlothian
Elizabeth dies in Dumfries in 1873…
Name: Elizabeth Brown
Died: 31st December, 1873, Penpoint, Dumfries
Cause: Phthisis pulmonalis
Age: 27 years
Informant: Robert Lawrie, widower
Father: Robert Brown, carrier
Mother: Elizabeth Foggo
…and Robert then marries Isabella Wallace.
Name Robert Lawrie
Spouse: Isabella Wallace
Marriage: 10th Dec 1874, Edinburgh Parish, Edinburgh
1881 census: 121, Links Street, Abbotshall, Kirkcaldy, Fife
Robert Lawrie Head 35 1846 Baker Edinburgh, Midlothian
Isabella Lawrie Wife 30 1851 - Earlston, Berwickshire
James Lawrie Son 5 1876 - Edinburgh, Midlothian
Agnes Lawrie Daughter 4 1877 - Edinburgh, Midlothian
George Lawrie Son 2 1879 - Edinburgh, Midlothian
Jessie Lawrie Daughter 0 1881 Abbotshall, Fife