“If you kill someone while driving drunk,...”
But they didn’t kill him. He killed himself.
He killed himself in part, because of actions they chose to do. They may not have intended his death as their actions, but they share much of the blame if they drove him over the edge. That's why I said manslaughter, not first degree murder. It is about personal responsibility on their part as well. Their actions led to a result, they should have personal responsibility for their share of the action.