If any lawyer here can give u details but i guess ur brother can come to Pakistan and get married. There is no requirement of divorce to get married for a man. Also separation have occured so no one can stop ur brother from getting married in Pakistan. I wonder what kind of dalla father is forcing they r married while his daughter wants divorce. File a new case with a good lawyer and collect all proofs n ask court to finalize divorce so that ur brother can take his new wife to Australia.