Hello! Welcome to BYC. I wanted to respond with a few suggestions. First off, you have three incredibley prey driven dogs, the one dog I was unable to train that I owned was a German Shorthair Pointer. Now I am not saying it cannot be done, and they cannot be taught, I have a Pit Bull who is great with my 5 chickens. My flock ranges in age from 10 weeks to 5 months. That being said, on to my suggestions. When my dog was young I made a point to teach him the command Don't Touch, and Leave It. He knows both of these commands WELL now, and whenever he is eating something bad I saw that and he drops whatever he had. This goes for the chickens as well. NO dog is bombproof around chickens, it's not IF they will kill, it's WHEN.
I want to defuse the idea that beating a dog with a killed chick will do nothing but make the dog smell deliciously like blood and chicken. The dog is just doing what dogs do, ESPECIALLY what they are bred to do.
I suggest keeping your chicks WELL away from any of your dogs until they are older. If I had a dog that was totally taken by my chicks, I would let them grow out to about 8-10 weeks. THEN I would start allowing the dog to view, smell, hear them through the safety of a secure as heck able fence. Please do not make the mistake of thinking you can 100% train your dogs to leave your chicks alone, they will not.
Even with my dog being as good as he is around the chickens, I never ever leave him unsupervised with them while they free range. I lost one wonderful Barred Rock that way. The dog had been fine until I went inside and BAM. Plus, the dog was proud as ever to have done something so "good". Dogs are predators, chickens are prey. You may have to make extra attention to your Aussie until the chickens are full grown. By then, as far as I am aware, the Aussie shouldn't be so prey driven or inclined to KILL them. But he/she may try to herd them.
But for now I would keep your chicks as out of sight as they can be from your dogs, just to give them some time to grow. I hope you aren't offended by my words about predator and prey, I am not aiming that to your dogs specifically, believe me. I just read so many stories regarding peoples own dogs being the worst predator.
It CAN be done so that your dogs and chickens can live in a harmonic atmosphere as possible, but it will take time, patiance, and firmness. No physical punishment is needed I don't think. The hose is NOT a bad idea though! Continue with that once you reintroduce them all again.
I hope this helped at all and good luck. Like I said I have a Pit Bull (prey prey prey driven dog) who can be with my chickens while they are free around the yard but I do not leave him out there if I come inside. He is always with me. I also did not let him around the chickens WITHOUT the safety of fencing until they were about 8-10 weeks old. Good luck!