I have found some informaton regarding your grandmother Clara Emily Wills.
She was born in Landrake, England in 1863 and died on the 2nd July 1944 at Habberfield, New South Wales. Her father is listed as being Frederick Wills and her mother Maria Polly.
As you said Clara married Donald Stewart in Orange, New South Wales. This took place on the 26th January 1884.
Donald Stewart was born on the 16th October 1853 in New south Wales and died on the 22nd August 1929 at South Kensington,Sydney, N.S.W.
His father was Kenneth Stewart and his mother being Ann Gordon.
The children of Clara and Donald were as follows:
Pearl Maria Stewart born 29-3-1885 at Redfern, N.S.W.
Clyde John Stewart born 1887 in Sydney.
Donald Edward Stewart born 31-7-1889 in Sydney.
I suggest you send for a marriage certificate and death Certificates for both your grandparents as this will give you all the necessary info you need to continue your family research.