Your ex's friends are idiots; the Hague Convention laws, in the majority of countries who participate, applies only to living children, not unborn children, as is the case in pregnancy.

You're not married, you're in Australia only on a partner visa, you're a grown woman who can produce a good income on your own, you have a supportive family back home, and right now you're very early on in your pregnancy. If you have the money and means to leave and you're 100% sure of your decision, do so NOW. It'll only get more legally and emotionally complicated the longer you stay in Australia, especially if your ex has the impetus to harass you and a gaggle of friends as a sounding board for his stupidity. You have enough stressful stuff to handle as is right now, and pregnancy is already one hell of a stressful process.

As soon as you get home to your family, please contact a lawyer who specializes in international family law and explain your situation, just so you're prepared for anything your ex might pull in the coming months, and once the child is born.

You're absolutely NTA here, and you are not, by legal definition, kidnapping anyone. You're just thinking clearly and protecting yourself and your unborn child.

Best of luck, please keep us updated