Relationship to me:- First Cousin, Twice Removed.
Registry of birth records show registration No. 27598/1885 for Halbert and 27599/1885 for Edgar suggesting Halbert and Edgar were twins. This is dispelled by the birth dates recorded in Margarets Bible showing the dates as recorded here.
Ida May was born in 1888 to parents Mathew Martin and Agnes Letitia and passed away in 1959 at Lake Cargelligo, New South Wales.
The only information for the children is unsubstantiated and suggests
Edward James born 1916 and died in1964.
John Robert born 1923, died 1996