With difficulty. The British Halfcrown coin has been issued since 1526.
Are your coins circulated (what condition are they in), mint uncirculated, or Proof?
Do you have a full range issued for a particular king or queen?
Do you have an example of every coin issued between certain years?
Does your collection include varieties?
I suggest that you take your collection to a reputable coin dealer in your area and ask for a valuation.
There was no 1805 British Halfcrown minted.
The last British Halfcrown was minted in 1970.
The last British Halfcrown was minted in 1970.
Halfcrown coins were never minted in Australia.
Australia has never issued a Halfcrown coin.
Such a coin does not exist. Australia has never produced a Halfcrown coin.
There were no British Halfcrown coins minted from 1865 to 1873 inclusive.
Such a coin does not exist. Australia has never issued a Halfcrown coin.
There were no British Halfcrown coins minted from 1752 to 1815 inclusive.
A Halfcrown is the eqivalent of Two Shillings and Sixpence. A Crown was Five Shillings.
The last British Halfcrown was issued in 1967 prior to decimalisation.
Such a coin does not exist. The last Eire (Irish) Halfcrown was issued in 1967. The Halfcrown was withdrawn and demonetised after the introduction of decimal currency in 1971.