I agree with what catastrophic said re: getting an order re: sole responsibility.
I'm not sure where you're at with legal side of things. Can you apply for legal aid re: sorting out the pre nup?

Glad that you can stay in the house til the bubs arrive. Not sure if somebody has already mentioned getting in contact with a student doula or student midwife to have some support through your pregnancy and there with you at the birth. Even if you end up having to have a c/section, it would still be great to have a support person in there with you, given your silly H won't be helping you. Even ask your current midwives at your next appt to help you find somebody, maybe sooner rather than later.

I hope Centrelink are able to help you on Monday