My daughter wants me to go to court next week with her against my grandson? What should I do?

I would go to court and ask the judge to order the whole family into counseling with/or probation on the offense. It is an alternative at many localities and it is sorely needed here. I would also not take a side. That would be an enabler. I would not expect a miracle if he did and refuse to take sides if it continued after. If you want to stop abuse in your family this is the start. If no effective intervention it is ped from one generation from the other in most cases and that is a clear pattern here. There is usually no easy solution. But this would be a start. In plain English the first step is they learn to deal with frusteration and conflict without physical actions....to each other. Or at least begin to learn that. When it has come this far it is hard to change this pattern of behavior.