In Aussie, if you sue someone for defamation of character is it up to them to prove their allegations? and is?

it necessary to disprove it? The mother and sister of my late husband (he died of AIDS but do not know I am not HIV positive) have been persecuting me and seriously defaming me over the businesses I have bought, built up, and sold, since his death. I had a hiccup with one which caused a temporary cash flow problem but nonetheless was settled out of court a couple of years later (not that they would know that). They have made up very serious allegations against my character, flying thousands of miles to my family to impart such nonsense. They imparted this nonsense to my young daughters, to whom I have showed my financials which disproves the claims, however they have caused me a lot of stress and heartache over their actions, and they still continue to do so with anything they can find. I want to stop them, not collect the damages, but because I am an extremely private person I am not willing to place my financials on the table for their scrutiny