+---James Trethewy (ABT 1681-)
+---William Trethewy (ABT 1714-)
| | +---Theophilus Coad
| +---Grace Coad 
+---William Trethewy
| +---Margaret Lang
+---John Trethewy (ABT 1779-)
| +---Mary ?
Catherine Trethewy (ABT 1827-)
+---Frances ? (ABT 1781-)