William J Slater

[majm]

NSW ER 1870 EAST SYDNEY
John SLATER, of Elizabeth St, freehold at 37 Botany Street
Josiah SLATER, of Elizabeth St, freehold House Junction Street
William J SLATER, of Market St, household 51 Market Street

JM

[mollipops1]

A William H SLATER and Sarah DENNIS married in Sydney in 1859 (reg 443), and I would contend this is the couple in the death notices and Sands directory, who had 2 children in the early 1860s.

Unless it is a 2nd marriage for Wm and Margaret had died? It certainly seems from W.H.'s death notice that he had an adult son in W.J.

A William J.J. SLATER married Mary BROWN in Sydney in 1858 (reg 950).

[mollipops1]

A William H SLATER and Sarah DENNIS married in Sydney in 1859 (reg 443), and I would contend this is the couple in the death notices and Sands directory, who had 2 children in the early 1860s.

Unless it is a 2nd marriage for Wm and Margaret had died? It certainly seems from W.H.'s death notice that he had an adult son in W.J.

Aha it was certainly a 2nd marriage for Sarah and this marriage notice confirms W.H.'s addresses:
http://trove.nla.gov.au/newspaper/article/13025563

There is a death for a Margaret SLATER in 1855 aged 47 that is not a bad fit...

P.S. This certainly seems likely to be the family from the original passenger list posted but the OP needs to come back and clarify the 'John and Sarah' as parents issue!

[mollipops1]

There is a death for a Margaret SLATER in 1855 aged 47 that is not a bad fit...

Yes this notice confirms this is the correct Margaret, wife of W.H. Slater, same address as death notice for daughter Mary Ann aged 10: http://trove.nla.gov.au/newspaper/article/60178647

[majm]

A Daughter to Mrs John Slater of William  St, Woolloomooloo
http://trove.nla.gov.au/newspaper/article/61324232  14 May 1853 Empire.

I think this would be a daughter for a John and Mary A SLATER, as per NSW BDM Early Church Records, 1853 Vol 39A (C of E) Line 184.  An ONLINE tree has the official transcription and so I add, that John SLATER was recorded on the ECR as a butcher, and his wife was recorded as Mary Ann SLATER.

https://familysearch.org/ark:/61903/1:1:XTCG-Q5J  Elizabeth Margaret, born 13 May 1853, baptised St James (C of E) 5 June 1853

JM

[Jamjar]

What are the parents names of John and Sarah?

You say the 'siblings' of their son William, what are their names?

Jamjar

[majm]

BOTANY cemetery as per family search … citing Sydney Branch Genealogical Library, Cemetery Inscriptions….

John Slater, aged 7, with father as Josiah and mother as Sarah.
Buried 9 November 1852

Sydney Burial Ground Reinterment register 1901
John SLATER died 9 November 1852, Wesleyan, Transferred to Bunnerong

History of Sydney’s Early Cemeteries Appendix 3
Wesleyan section
Family Grave SLATER
Sarah died 6 October 1852 aged 9 years
Mary died 29th October 1852 aged 17 months
John died 9th November 1852 aged 7 years
Sarah, wife of Josiah SLATER died 5th June 1855 aged 38 years

JM

Slater seems to have been a popular surname in Sydney and surrounds in that era. 

[maddys52]

Death notice for Sarah
http://nla.gov.au/nla.news-article12970087
"At her residence, Elizabeth Street, on Tuesday the 5th instant, Sarah the beloved wife of Mr Josiah Slater."

and funeral notice
http://nla.gov.au/nla.news-article12970138

[maddys52]

I'm hesitant to do too much more research until we hear back from Tom, however there is this on Trove:
http://nla.gov.au/nla.news-article13002077

A Josiah SLATER paid the deposit for the passage of Joseph, Elizabeth and Maria SLATER  who arrived on the Boanerges in October 1857.