The Barony of Roslin went to his first son by that marriage , Sir Oliver Sinclair .
The earl 's second son of his second marriage , William Sinclair , became the designated heir of the Earldom of Caithness , and continued that title .
The Barony of Roslin went to William Sinclair 's first son by that marriage , Sir Oliver Sinclair .
The earl 's second son of his second marriage , William Sinclair , became the designated heir of the Earldom of Caithness , and continued that title .