This is from the Australian Marriage celebrant site.
Can you be related and get married in Australia?
The following relatives can not get married by lawe in Australia:
a person and an ancestor or descendant of the person
a brother and a sister (whether of the whole blood or the half-blood)
a person who is or was an adopted child, and, for that purpose, the relationship between an adopted child and the adoptive parent, or each of the adoptive parents, of the child, shall be deemed to be or to have been the natural relationship of child and parent.
Which basically translates to this: you cannot marry your parent, great/grandparent, child, or great/grandchild, brother or sister, blood or adopted.
So the other side of that list leads you here. Which relatives can get married in Australia?
uncles or aunties
cousins, first, second, and onwards
step-siblings or step-children
in-laws
foster siblings or children
almost all other people