Sharon,
Alexander Ogilvy, younger of Inchmartine, may well be the son of Mariota Hay, since he was the lawful son and heir of Sir David Ogilvy of Inchmartine, and Mariota Hay was Sir David's lawful wife, but proof of relationship is wanting.
In this regard it should be noticed that Alexander Ogilvy, younger of Inchmartine, is first noticed in two charters dated 6 August 1480 [links below], when he ratified his father's gift of land to his bastard sons, James Ogilvy, and David Ogilvy, and Mariota Hay is not noticed as the wife of Sir David Hay of Inchmartine until 30 April 1492, when she gave her consent to her husband’s gift of an annualrent to the Friars Minor of Dundee [link below]. Sir David must have secured a liferent for Mariota on his lands of Petmedill and Inchmartine before this date, but exactly when he did this, or if it was prior to the birth of his son Alexander, is not yet clear.
https://catalogue.nrscotland.gov.uk/nrsonlinecatalogue/overview.asp...
https://catalogue.nrscotland.gov.uk/nrsonlinecatalogue/overview.asp...
https://archive.org/details/registrummagnisi02scot/page/613/mode/1up