Judith,
I have completed a book on the Helyars in Australia from 1841,when the "Ferguson" landed in Port Phillip.
The twins,Ellen and Martha,were born in England 2/10/1839.The ship departed Plymouth 21/9/1840 and the mother,Martha, died 9/10/1840 aboard ship with her twin daughter,Martha,and were buried at sea.
The other twin,Ellen,died 27/4/1841 due to a choking incident near Melbourne.On the same day the "Ferguson" foundered on a reef in the Quoin passage on the far north of Queensland.
I know your message is four years old,but it would be great if you could get in touch with me as your records may hold important data for my project.