Hi there,
From Daniel and Alice's m.c. does it show on the far right that the information re their parents was added to the NSW BDM registrar's records in 1912 or thereabouts? (only to confirm that this had been reconciled, and thus the information about their parents was added to the NSW BDM registrar's records some 30 years later)
From your Grandmother's m.c. it shows Daniel as deceased and that Alice was therefore alive at that time, and was known as Mrs Scott. So from that, it would be sensible to consider searching for her death at sometime after the marriage of your Grandparents and under the surname SCOTT. The information on m.c. is based on information given by the bride and the groom to the clergy. Its accuracy was not checked by the clergy, but the bride and groom give the information in good faith. (edit to add, and as the father was deceased, the clergy should have asked if the mother had re-married ... and that new surname should have been noted on the m.c.)
Where and when were your grandparents married? Is it likely that Alice would have attended the wedding, and perhaps lived with the couple after that marriage .... Have you found your grandparents on the electoral rolls? Have you then looked at those rolls to see if any others were at that same address or nearby? (a difficult task, as Australian rolls as by surname and not by address at various online commercial sites).
Cheers, JM