I am going to guess that yours are between 6 and 8 weeks old. They all look like pullets to me. Here is a pic of my Aussie girls when they were about 6 or 7 weeks old.
They all look like pullets to me. They look like their around 6-8 weeks old. They are fine to move outside if you have the proper shelter arranged for them
You can go ahead and put them outside. They look to be feathered enough. If you are having a cold snap, you might want to use the heat lamp at night on them, a few feet above their heads. Just enough heat to add some warmth. If the nights aren't too cold, they won't need any more heat at this point.
Good luck with your new Aussies! They are a great breed and friendly up very easily.