There is a will for John Mickle LYALL (which you probably have), of Tooradin, died 18 December 1925. The will is dated only 2 days earlier than his death.
Probate is granted to his wife Medora LYALL and son Harewood LYALL, motor mechanic, both of Tooradin. he does not name any other children but states that on the death of his wife the property should be divided among any surviving children.
If you look on the white pages you will find entries for LYALL in the general area - Cranbourne, Langwarrin etc, although I see Harewood in South Melbourne by 1977. They may not be related but would be worth a call or a letter I would have thought.
According to the birth entries Harewood was a son of Cecil and John, b 1899.
I see this death entry
Victoria 1985 #28722
Sheila BLACK, 78
Died: Dandenong, Victoria
Age: 78
Father's Name: John Mickle Lyall
Mother's name: Madora Bisane
Estimated birth year: abt 1907
Victoria 1902 #13464
William Geoffrey LYALL
Died: Dandenong, Victoria
Father's Name: Jno Mickle Lyall
Mother's name: Cecil Garnet Carr
He is buried at Cranbourne
Sorry, not much help and you probably have all this.
