Black Australorps are definitely cold-tolerant. They'll handle below 32 just fine. Then can even handle below 0 degrees. I don't know your setup, but the only cold-related things you should be concerned about are (a) giving them a way to get away from snow/rain, particularly when they are sleeping and (b) avoiding drafts directly blowing on them when they are sleeping while maintaining good ventilation.
As for heat, the keys are to provide open water so they can drink deeply and good shade.
---------------
I've had mixed-breed flocks and the Australorps are some of the more likely to become broody, so if you have any roosters, you can certainly get them to raise future generations for you. You might want to invest in leg bands (size 11/16mm) to help identify them by year born.
3rd year chickens still have plenty of laying in them, but not enough to be commercially competitive. I've seen shady people selling them as new layers, but if you are honest about their age, you will still be able to get rid of some cheap or free and lower your costs.
Just to be clear about the "tough" birds. 18 month-olds will be tough. Commercial producers will generally sell them for pet food or other uses. The more tender broilers that you buy in a store (either cooked or raw) are generally from 2-3 month old meat-bird hybrids (Cornish Cross) that are super-growers and haven't had time to toughen up.
Edit: If you do decide to let your girls raise chicks, then you will obviously get ~50% roosters. You'll be able to harvest the majority of them young for food while keeping the layers.
they have stuff put up to block wind, no heat or anything though, and they seem just happy and content. I have 12 roosters because I read that it's suppose to be 10:1. Only problem I have is this crazy little bb red bantam rooster, he's wild, and tries to fight the Beilfelder roo, the Speckled Sussex roo, and one of the Black Copper Maran rooster. Never seen anything like it. And I really do appreciate the help. Leg bands are fixing to be bought 
