How often have two Representatives members — including former mps, not just those currently sitting — voted the same way on the same piece of legislation? Based on the Australian Parliament's own division records (aph.gov.au) — see About for the method. Representatives and the other chamber can't be compared to each other: they never vote on the same motion, so there's nothing to compare — compare Senators on their own page.
Prime Minister vs Leader of the Opposition
Anthony Albanese and Angus Taylor couldn't agree on what day it is.
(agreed on 3.2% of substantive votes)
Data: Australian Parliament division records, aph.gov.au • see Anthony Albanese or Angus Taylor's full summary page