I'm so sorry you have to go through all this
Reading your story I'm holding back the tears. You had a tough decision to make, but you did the right thing. It's no fair for Scooter to be in so much pain.
Regaurding the german shepard, I would call animal control. Even if it is your brothers dog, this dog already killed one of your babies, and like you said, your worried about your daughters safety. What if he attacks another dog in the neighborhood? I know it'll be a hard thing to do, but if your family isn't doing anything, I would take it into my own hands and call the animal control. Better to be safe than sorry.
I'll keep you in my prayers that your able to make it though such a difficult time.