These are way outside my area, but I'll add what little I can.
These stamps are from the State of Western Australia. As they're denominated in £sd, they must date from before 1966.
The 'Probate' on the stamps refers to a State tax on the value of property left in a will. In Australia, and elsewhere, wills still have to be 'approved' before the State Supreme Court before they can be put into effect, and the property can be divided up between the heirs. ('Probate' comes from the Latin
probare, 'to approve'.)
Member Rod222 would be the ideal person to comment, since he collects Revenue stamps and lives in Western Australia. I don't seem to have seen any contributions from him lately. Is he OK?
Failing that, you could take a look at this Web site for more information:
www.ozrevenues.com