This appears to be Selina A[nn]'s birth and her siblings' birth regs [including a brother Alfred...see electoral roll below]
http://www.rootschat.com/links/0dqw/Her parents' marriage - parish record
V1845232 77/1845
COBBY George
LAVETT Jane
JB = Presbyterian St Andrew's Scots Church, Sydney
William and Selina's children's births
http://www.rootschat.com/links/0dqv/Any of the chn's birth cert should name Wm's place of birth.
New South Wales Electoral Roll 1903
NSW/Parkes/Strathfield
SWEET Selina Richmond Road, Flemington Domestic duties
SWEET William Richmond Road, Flemington Labourer
SWEET William Thomas Richmond Road, Flemington Stamper
and also
COBBY Jane Richmond Road, Flemington Domestic duties
COBBY Alfred Richmond Road, Flemington Labourer
1930
SWEET Selina Anne 90 John Street, Lidcombe HD
Her death
15316/1935
SWEET Selina A
Father John Mother Jane
District Hornsby
As Selina is the only
SWEET at the 1930 listing I wonder if this is William's death
6079/1929
SWEET William
Father William Mother Ann
District Auburn
Cheers
Cando