Email the brother and say,
"Just as I could not help him, I cannot help the family." Your best bet is for each of you to either get private counseling or go to Alanon FOR YOURSELVES."
You are out of it, you know that. You know the 3 C's. You did your best.
Please, as much as you still care for the man, you KNOW. So continue to work on you, say a prayer that their HP's will guide them.
J M H O
Love and hugs,