Which Australian state were they living in? Most states have very good records, with NSW giving full details of parents and addresses etc even on death certs. I suggest you buy John Nelson Gill's birth cert., and then his parents' marriage cert from the details given on the birth cert., then their birth certs from the details given at marriage, etc. - going back to the first person who arrived in Australia, and the parents on that person's marriage and/or death cert. Then let me know the details, because I have a lot of Joughin records up to the mid-1800s.

Sue