Stewart's death certificate available online gives his birth date as 16 November 1854. Does this match the birth that you found in Belfast in 1853? Also, since civil registration did not begin in Ireland until 1864, from what source do you have the 1853 birth?
Thomas Thompson & Catherine Gawley were married in 1852 in Ballinderry, Co. Antrim. You might want to check the parish records there for the marriage of Stewart & Sarah.
Also in the list of children you have for George & Elizabeth, you have more than a 20 year gap between Stewart, born 1853 and Mary Jane born 1876. This likely suggests two different couples with the same names.
The eldest child of Stewart & Sarah was born in Halton County, Ontario, according to her birth registration. The next three were born in Manitoba (per 1901 census). Only the youngest two were born in BC.
Stewart and son Norman made a trip home to Ireland and returned to Vancouver in 1912 via New York.