The parents of Duncan Smith are Isabella Smith and Isabella Smith
Sources: 
Death Record of Duncan Smith (1855)
From https://hebrideanconnections.com/record/people/107964/
"Duncan (1803-1855) was a son of Malcolm Smith and Isabella Maclennan. By 1820 his father's name is on the rental list for Buanish and by then the family were settled at 5 Buanish.
In 1826, when Buanish was cleared, the family lived with his uncle at 8 Tong.
At Stornoway, in 1832, he married Henrietta Macsween of 16 Tong. Duncan and Henrietta settled at 1 Old Gearraidh Ghuirm where they had three of their nine children.
Old Gearraidh Ghuirm was cleared in 1840 and the family moved to 5 Tong."
from https://hebrideanconnections.com/record/crofts-and-residences/111359/
5 Thunga
The first tenant of 5 Tong was Duncan Smith (1803-1855), son of Malcolm, 2 Tong and he passed the croft to his widow, Henrietta Macsween (1812-1882) and she passed it to their grandson, Malcolm Smith (born 1851).
In 1895 Malcolm Smith sold the croft to Malcolm Macleod (1866-1954) son of Alexander, 28 Aird Tong and moved to Steinish.
Malcolm Macleod passed 5 Tong to his son-in-law, Malcolm Murray and in due course 5 Tong passed to his sons."
In the NEGHS article for Trump's ancestry, they do not give Duncan a death date. This implies that they did not find the death certificate linked above, which is why he has no parents listed in the publication. Also, they appear to have neglected to look at the local histories of this region, as the individual crofts seem well documented on the Hebridean Connections website. I will poke around a bit in the other families in the tree, maybe we can expand some of the other branches of the ancestry as well!
