How to file divorce

Hi, my brother got married on 27th Nov 2017, after few months his wife started abusing my parents with nasty words again and again. After few months when my brother could not control hearing all these nonsense, he slap her. She filled police complain and police has taken apology letter from my brother. After this incident, my brother did not agree to stay with her, because he felt she is mentally challenge and can do anything. Its been almost a month they are staying separately and has no contact. What we get to know from common friends, she always threatened saying she will file a case again domestic violence, also we get to know she is trying hard to get her PR Australia and leave this country. We have approached her to get divorce and leave country, but she is not responding. Their marriage did not registered, just submitted one application. It will be really helpful if someone help me to get divorce from her and also let me know the process. She is working women earning 60K per month.