Megan, you can buy his NSW death cert online, which should give a lot of details you can then follow up to get back to earlier generations. As well as name, occcupation, age, residence, it should give where born and length of residence in Australia, names of both parents including mother's maiden name, and dates and details of his marriage and children.

The index at http://www.bdm.nsw.gov.au/familyHistory/search.htm has:
[reg. number and year of death]: 25526/1950, [last name]: SKILLICORN, [given name]: RAYMOND, [father's given names]: BERTIE PHILLIP AUBREY [mother's given names]: AMY LUCY [district]: BURWOOD.

His marriage cert would also give useful information. There is a 1947 marriage in the index [you will know whether this is the right one?]:
21545/1947 SKILLICORN RAYMOND [marriage to]: MORAN, MARY ELIZABETH, SYDNEY.

Also a 1907 marriage:
8972/1907 SKILLICORN BERTIE P, [marriage to]: JONES, AMY L, [place]: WATERLOO.

And an 1879 birth:
9571/1879 SKILLICORN, BERTIE PHILIP, [father]: PHILIP, [mother]: SARAH, [place]: BATHURST.

Bertie's death cert will give all his other children as well as Raymond, plus the details I wrote at the start of this message which will confirm his parents.

Death:
18349/1945, SKILLICORN, BERTIE PHILIP AUBREY, [father]: PHILIP AUGUSTUS [mother]: SARAH, [place]: MARRICKVILLE.

This looks like Philip's marriage, in 1877:
2176/1877 SKILLICORN PHILIP, [to]: PATTERSON, SARAH, [at]: BATHURST.

So, to get earlier than Australia, and also to find all the descendants of Philip Augustus, you need to buy as many certs as possible, because all will have snippets of information not included in the others. All the above give you the option to "buy now" online.

Sue