+---James Trethewy (ABT 1681-)
+---William Trethewy (ABT 1714-)
| | +---Theophilus Coad
| +---Grace Coad 
+---William Trethewy
| +---Margaret Lang
+---William Trethewy (ABT 1773-)
| +---Mary ?
Ann Trethewy (ABT 1803-)
+---Philippa ?