"You're aware that Canada or Australia would need no consent from
Westminster (or, more specificaly, the Westiminster Government) to
become republics (afaik, and even if they do it's highly unlikely that
permsion would be denied)?"
The Monach's viceroy of Canada has the legal right to depose(fire) the prime minister of the country. AFAIK this is true of any of the commonwealth/empire nations. The viceroy can dissolve parlaiment, and has other rights superior to those of the prime minister.
There is no federal executive branch(directly elected leadership) in these governments except for the monarch and her viceroys.
"You realise that if a member of the royal family even so much as makes
a political sounding statement beyond the carefuly prepared speaches
they read at new year and the like they get attacked by the press and
politicians for abuse of position right?"
The Queen has the legal right to appoint people to her crown corporations or to use the money to do whatever she wishes. Most of the time this is done through appointees. The government pools the money in right of the Queen in a trust under her name. She can legally veto legislation and she can seize property by right of the federal government.
These are all within her powers.
The British monarchy had forced conscription in WWI for example.
"You're aware that if the monarch tried to even use their residual power they would be imediatly deposed of by parliament?"
The mere fact that they have residual power can be taken as an indicator that those in the commonwealth/empire countries would attempt to overthrow or succeed from the federal governments if it stood on it's own. That's why the monarch picture is still on both the paper and coin currency.
They never directly abuse the power. They do it with indirection as not to alarm the royal subjects. By mentioning royal subjects I am not using a euphemism. The people of those countries are literally royal subjects. The ministers including the Prime minister must take and honor an oath to defend the monarch and her family to the death and is inaugurated by her viceroy.
The British house of lords* is not elected, but rather appointed or selected by other wealthy members symbolic of landowners in the medieval times.
*(the upper house where the parlaiment is the lower house of government)