ok, i'm gonna look at BEFORE baby is born cos it sounds like there is more to this than JUST after baby is born

if you are currently living in a marriage like relationship (defacto) then you need to tell centrelink NOW - or if you move in together, from that date. you say one person is on Centrelink payments NOW - if you don't declare, that person is being overpaid every day and it's possible you will be caught out and end up with a nasty little debt. partnered status doesn't apply JUST after the baby is born and for baby related payments - it's an "all the time" thing - so you need to notify NOW otherwise she is being overpaid for newstart/youth allowance or whatever payment she is currently on

as for after baby is born - you're defacto, so you will be treated as a couple. current income (his 45k) is too high to qualify for parenting payment (income support) but you will qualify for baby bonus and family tax benefit. you'll get the forms when baby is born. at the MOST, you'll get around 150 of ftba, and, if partner does not have any income (including centrelink payments) next financial year, around 130 of ftbb. if you're paying rent, you might get rent assistance - but if you're paying board to one of your parents, what you get for that "rent" amount will be taken into account both for you and for the parent. if it is deemed rent, it is deemed income for the "landlord" so make sure you have an agreement in place with that one.

don't try and say you're not partnered when you are - it really isn't worth it. there are many factors apart from the room you sleep in that will determine your partnered status and if you say you're not partnered when you are, there will be nasty debts and potential prosecution for defrauding the government - soooooo not worth it