Not knowing the extent of their injuries, I couldn't advise you on what you should do with the survivors. Being an animal owner, you need to decide if they are suffering or not, and if you are keeping them alive because they will have a good quality of life, or if you are keeping them alive for your own feelings. This is something everyone should think about when they have animals of any kind. And I do practice what I preach here. We had to put down our 10-year old lab this summer. It broke my heart, but he had gotten cancer in his mouth, the vet wouldn't touch it (he said that it was contained and was worried that if they messed with it, it would spread). Well, it got to the point where I had to wet down his food because he couldn't chew well and then the tumors started bleeding. DH and I both decided that he deserved better than that, so when I was leaving for a week, DH waited until I was gone and then took care of the dog. I have also put down chickens (well, I haven't, but have asked DH to do it - I would if I absolutely had to) that were sick or injured because I learned the hard way that most of the time, "trying to make them better" only prolongs their suffering before they die anyway. So, you have to ask yourself if they are in pain, if they will be able to function this way, if they will always be suffering or if they will heal. If you decide that you want to try to fix them, then you need to think about how long you are willing to work at it, and if you are really helping or not. It's not easy. It's one of the hardest parts about having animals. Just remember that sometimes the hardest thing for us to do is the kindest thing is for the animals. If you feel they need to be put out of their suffering and can't do it yourselves, find someone who can. 
 
If chicks can still function (eat, drink & move around), no need to put down. I've never had any birds survive a predator attack.
 
I would say if they can still function WITHOUT UNDUE PAIN AND SUFFERING  on their part.