Robert Colthart was born in Lanark County Scotland around 1827. On January 21, 1854 he was united in marriage to Jane Ritchie in Lesmahagow. Robert and Jane had at least one child: Margaret (1861). Jane died on September 2, 1864 in Lesmahagow and Robert married his second wife Marion Robertson in 1865. Robert and Marion had at least four children: Marion (1869), Jeannie (1873), Annie (1875) and Thomas (1878). In 1881 the family was living on Kirk Street in Strathaven where Robert worked as a van man. Robert died in Avondale on May 20, 1898.

• Margaret Allan Colthart (1861-) was born on February 4, 1861 in Abbeygreen, Lesmahagow, Scotland. At age 19 she gave birth to her only child: Thomas (1882-1953). Margaret was a domestic servant when Thomas was born. She married John Arrol in 1889.