Wow, you are going to have your hands full. I have never raised two puppies that close in age but maybe someone with more experience can chime in.
As far as keeping your GSD from rough housing, I would keep him on a leash and with me even in the house. Your Aussie is very young and getting tackled by such a large puppy could cause behavioral issues or injuries.
♥ Faun GSD 12-22-13
♥ Daisy Rat Terrier/Beagle Mix 3/15/02