At the time of his 1838 marriage to Mary McNab, second daughter of James McNab, Robert Cassels was Manager of the Bank of British North America, Mirimichi. He purchased two parcels of land totalling 364 acres on the eastern side of the island in partnership with Captain Lyttleton. Prior to Lyttleton moving to New Zealand, Robert Cassels purchased his brother-in-law's interest in the two parcels of land which they jointly owned.

On November 25, 1878, Allan Cassels bought out his father's interests in the island. For several years he leased portions of his property on McNabs Island to Byron Newcombe, a dairyman from Eastern Passage.Allan's brother was The Honourable Sir Walter Gibson Pringle Cassels, Chief Justice of the Exchequer Court of Canada. Their sister Margaret, along with her husband A.H.Cook, were the authors of an interesting letter to Allan's daughter, Chelsea, which describes the history of McNabs Island.