I don't post often (I only just remembered I was a member here!), and breeding and chick raising is not my area of expertise. I'm just an owner. Having said that, firstly, I'm very sorry to hear that you've already lost 2 chicks.
Sailboat is right, you need to be trained in how to successfully feed the remaining chick once it is hatched. Not all animals automatically know how to be good parents, and it sounds like your breeding pair may have missed some of that information for whatever reason. It's a fallacy that all animals automatically know how to raise their young, and that includes birds and humans. Some of us just suck at the whole raising offspring thing and require some outside help.
If you cannot find or afford an Avian vet in your area, then hit Craiglist or a local bird forum and beg for support from a local breeder who has some experience in hand rearing. You'll need to learn a lot in the next few hours if you're going to be able to save the remaining chick. I know Australian bird groups are very supportive of their members, so I hope that the bird groups around you are also. Try and find a breeder you can visit, or who might come to you and at least assess your chick every now and then too. There are a few ways to go about it, but Sailboat is right, it's up to you now.