I had seen Josiah Oake Treeby but was always confused about the Oake bit - he has never been referred to as Josiah Oake Treeby in anything else I have seen! I will order the death certificate and see whether it is our man! Maybe Henry Treeby senior married a female called Oake (there are plenty of people called Oake/Oke etc in this area)
There is a Hephzibar Tribe who died in Bradford (Yorkshire ie North of England) in 1854 but not sure whether that is Josiah's wife - seems like she had 3 children before she married Josiah but I cannot trace any of them.
I have located Elizabeth Treeby in 1851 Census - living with Josiah, Samuel and Elizabeth in Plymouth - it is difficult to see whether she is a widow (someone has drawn a line through that bit!!)but she is said to be the head of the family and is working as a launderess - do you know when they went to the USA?