We have one census record for Gabriel and from this we know that Gabriel Crosbie was born in Glasgow in around 1799. We have several census records for Mary Thomson and we know that she was born in 1805 in Rothesay in Bute. We don't know the parents of either Gabriel or Mary.
In 1851 Mary and Gabriel are living in Barony in Glasgow at 2 Anderston Quay. Gabriel is a journeyman painter. They have none of their children staying with them.
In 1861 Mary is in Greenock East in Renfrewshire at 8 Baker Street. Her daughter, Jane Walker, is with her with two children John,3 and Mary,1. Mary states her occupation as Sick Nurse.
In 1881 Mary is 77 and living back in Rothesay in Bute at 14 Argyle Street. She states her occupation as House Letting. She has her grand daughter Jeannie Walker living with her.
Gabriel presumably died between 1851 and 1861 and Mary between 1881 and 1891. The Hogg Barnes tree on ancestry.com shows Gabriel dying before 1856 and Mary dying in 1888.
The only child we know about is Jane or Jean. She was born on 10 May 1834 in Glasgow. She married Andrew Walker sometime around 1855 and had her first child, Annie in 1856. She had 5 other children and died in 1874, which I know from Alex's tree.