I'm sorry this happened... The same thing sort of happen to us, in that a neighbor's dog kept getting out of his yard and coming up and terrorizing not only our dog, but us as well. He charged my stepdad and brother, and finally we had to sit down and talk to the owner, telling him that if this kept up, we'd have to go to the police. Thankfully they patched up the break in the fence, and that was that, but it was a scary time. He was a brindle, and this took place in fall, so it was very hard to see when he was out there. It was terrifying to go into our own backyard. If we hadn't done this, I imagine we might have ended up with either a dead dog sometime, or injured people.
I'm extremely sad that this happened to you, but the honest truth is is that it was NOT your fault. The dog invaded your dog's territory, and so was trespassing. This means that I do not believe your family can have charges brought up on them. The only thing you can really do is talk to the guy, ask him if there's anything you can do. Otherwise something you do might just make the owner angry. Once again, sorry that this happened ): I hope everything works out.