1. This question in simpler words is asking how the constitution can stop the federal parliament from exercising certain laws. The constitution limits the powers of the Commonwealth Parliament or federal Parliament in many ways. The Commonwealth Parliament cannot initiate legislation where the state has residual power. Moreover under section 116 the the Commonwealth cannot make laws concerning the establishment of Religion.
2. I believe you should start of with "a referendum is the only way to change the actual wording of the constitution". Than proceed to give a short explanation of the "process of a referendum". For example, suggestions for a change to the wording of the constitution arise, the change to the wording is drafted, The bill can than be passed through both houses parliament or a majority in one house which than requires approval of the Governor General. In order for a referendum to be successful, it must meet the requirements of section 128, which require a majority of 'yes' voters (50% and more) while also gaining a majority of states/territories (4 out of 6 states). However if the referendum does not meet the requirements of section 128 and does not obtain a double majority, the referendum will fail and therefore the wording of the constitution will remain the same.