He was married three times: in 1762 to Margaret Oakshott, in 1768 to Mary Burrows, both at St Martin in the Field and in 1781 to Clarissa Doran at St Luke, Chelsea.
Mary and Sarah, children of Sebastian and Margaret, were christened at St Martin’s in 1764 and 1767 respectively.
In 1769 he paid Duty as a silversmith for the apprentice indentures of William Robertson junior.
Honor and Honorius, children of Sebastian and Mary, were christened at St Martin’s in 1770 and 1772 respectively.
His daughter Sarah (1767-1824) married Robert Garrard (1758-1818) (Grimwade p.519) at St Martin’s in 1789.