The Colquhoun name seems to have been transcribed with many spelling variations, including Colhoun, Calhoun and Colqhoun. Colquhoun is the spelling recorded in the early records.
Robert was born about 1622 and was the only son of Adam. He was described as Robert Colquhoun of Corkah, County Donegal. He married his first cousin Katherine, daughter of John McCausland and had three sons and one daughter. 
"It was in the person of this Robert Colquhoun that our branch of the family found its way to Ireland"
It may be possible to confirm family relationships with Robert by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree: