Thanks Jean and Gordon for your reply.
We have purchased Margaret Eliza's birth certificate and the only info contained is date of birth, in District of Hamilton, and father and mothers name only. We have also purchased the marriage of George Thomas JACKSON and Catherine SHAW in 1873 the only info is date, name, age and rank and when registered in the district of Hamilton, so hasn't been any help. We also have purchased after a wild guess, the death of Catherine in Victoria in 1875 with the info we would usually find on Vic certificates, including a daughter Louisa 2 1/2 years, Margaret Eliza 18 months and William 5 days. We also think that William born 1875 may have died in 1876, but the death index on Ancestry says father U, and that he was 5 months, so haven't bought that certificate as yet. The informant on Catherine's death certificate is Alfred Jackson brother in law, who also registered the birth of William. We haven't been able to establish whether George died in Victoria as lots of possibles, but we know that he was deceased on the second marriage of Margaret Eliza in 1906 in NSW.
We think that maybe George remarried to Hannah Quigley in NSW, but was hoping to try and find parents, and maybe a death certificate to cut down on the costs. Thank you both again for your help, you are both awesome. Regards Janet Hutchins.