Brent ....do we actually have the births details of two different people ie Joseph
William TINKLER and Joseph
Walter ST CLAIR
From family search
ST CLAIR Joseph
Walter Birth 30 Oct 1876 Auckland,
New Zealand Father George St Clair
Mother Bridget
and
TINKLER Joseph
William born
Tasmania with parents William ST CLAIR and Sophie GILES

You really need to follow tropicalj's advice and download the marriage certificate of Joseph TINKLER and Elspeth STEPHENS.
The only STEPHEN/S birth in 1869
STEPHEN Elsie
Father Charles Patrick
Mother Mary Ann BERGIN
Birth Place SANDRIDGE 1869 Reg# 11465
I wonder if Sophia who married 1st Michael Molloy, 2nd Stracran Tinkler, had anything to do with William St Clair of Hobart Tasmania??
This may also be a useful death certificate even though no parents' names are known, it should detail her marriages and children of same.
TINKLER Sophia
Father Unknown Mother Unknown UNKNOWN
68 years Death place Melbourne East 1899 Reg# 6652
Cando