Hi,
If you obtain a transcript of the those marriages, (Phoebe's and her Mum's) (I would not be ordering the real deal cert, the transcript will be cheaper, quicker and contain exactly the same info, including most likely some blanks as many of those rural/regional mc are not yet reconciled at NSW BDM HQ) it may just help, as it will give you the clergy/denomination for the ceremony/ies. From that you can then proceed to search for the original parish records, which should include the names of both sets of parents, the ages of the bride and groom, and all the usual family history information that will validate the current online submitted trees.
I my view, the two transcripts for those marriages should cost you around the same fee as one real deal certificate from NSW BDM.
Cheers, JM