I'm sorry for your loss and the difficult situation you find yourself in. It is kind of you to consider how would be the best way of telling your brother; you've taken on a good deal of responsibility by taking the lead in letting him know.

Here is my advice, and that of my wife who has spent twenty-four years in prison during our thirty years together...so unfortunately, we know a bit of what we speak. Call the jail and ask to speak to the chaplain. In almost every state, the procedure is for the chaplain to facilitate a phone call where you can tell your brother over the phone and the chaplain can be there to assess his emotional needs.

I hope that helps and again, I'm sorry for your loss.