"The Genealogical History of the Noble Family of Courtenay" pp. 134-5 states that Sir Hugh de Courtenay, Lord of Oakhampton inherited property from his "Uncle William de Courtenay" whose lady was "a daughter of Thomas Bassett".
However, on Geni their father John de Courtenay, Lord of Okehampton has no brother "William de Courtenay" married to a Bassett woman.
Instead, the only uncle William they have is William de Preaux , for which no sources have been provided.
And this William has neither wife nor sources shown here.