Suggestions
1. Email C of E at Coonabrarbran and ask them to check if they have (or have a record of having had) Coonamble's register OR do they know who you can ask
2. Email C of E at Bathurst (Diocese HQ) AND ask them the same
3. Email the various family history groups explain what the NSW BDM have supplied you with, and can they help (or know where/who you can ask) to fill in the blanks
4. Find another mc for Coonamble for 1875 or there abouts for a (make a good guess) possible family member, or for the witnesses to Esther and George's marriage .... You are aiming at assuming Esther had siblings (unusual for a lass born c 1859 in NSW NOT to have siblings) ..... You are looking for a lass YOUNGER than Esther, and hoping that the bit on that newer mc will include the name of the person giving consent to the marriage (I am presuming it will NOT be a reconciled mc, thus of little value to family history, but that ONE clue could help CAUSE .... perhaps George Creighton or Esther Creighton were witnesses to that marriage

or perhaps Esther's parents were witnesses (you still won't be able to prove that relationship BUT it is one step closer). I call that the LEAP OF GUESSIMATING rule ....

cause it really is NOT the 'right' way to research.
Re middle names ... and to expand that pool .... sometimes the godparents names are included in the child's name !!!
I think you need to get to the NSW SRO to look at the Deposition registers to find further info about the children, and perhaps to find Esther's admission to Coonamble Gaol etc. I don't think there is much more available from the armchair

PS, Next NSW BDM mc, MY TIP .... Well I would be into trying to save some pennies and get an official transcript, same info as the real deal, and you may need to get several more ...
Cheers, JM