III. John, only son and apparent heir of Sir John Sinclair the first baronet of this family, being by his father put in fee of the estate of Stevenson, married Isabel, daughter of Robert sixth lord Boyd, by lady Christian Hamilton his wife, daughter of Thomas earl of Haddington; and got a charter under the great seal, Johanni Sinclair feodatorio de Stevenson et Isabella Boyd ejus spouse, terrarium baronie de Stevenson, etc. dated 14th July 1638.
By the said Isabel Boyd he left issue two sons.
1. Sir John, who became his grandfather’s heir.
2. Sir Robert, who carried on the line of this family.
He died before his father, and was succeeded by his eldest son, Sir John Sinclair IV, 2nd Baronet of Stevenson who died without issue. The line then succeeded with Sir Robert Sinclair IV, 3rd Baronet of Stevenson.
