That's an interesting point about the multiple wives thing . I have no idea how that works legally or whether it is actually allowed in Australia .
Similar to men marrying juveniles . It obviously can't be legal here as the minor wouldn't have the legal rights of an adult .
But , I agree with you that there should be clarification . As far as I know it is about marriage between one adult to another of the same sex . That would preclude the variations that you've mentioned .
Maybe this question will highlight some other issues that need to be dealt with such as adults marrying children ?