Letting go is part of the battle. And also praying violent prayers for our loved ones.
It used to scare me when I would pray, "Lord take them where they need to go, to get to where they need to be with You". And even now, I admit, I feel a twinge when those words come out. "What if they die? What if they get hurt? What if....?"
Is their life right now so wonderful, as they might be abusing themselves, hurting themselves, and others? No. So what could be any worse? I know that this sound harsh, but as I have gone through addiction recovery with one family member, and other things in a marriage, don't I know that God wants the best for them? Don't I know that God wants no one to perish, but to come to repentance and to the knowledge of the truth?
And how do I think that He will do that? Will He let them perish? The Word says in 1 Tim. 2:4, "Who will have all men to be saved, and to come unto the knowledge of the truth." And in Acts16:31, "The Lord is not slack concerning His Promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance." (Thanks to my mentor who keeps the spirit of slap ready in my memory work - Kidding!)
But reality? God loves them more than I do. Reality? His plan for them is better than mine! (Yeah, I admit that my plans could be a little vindictive!) Reality? God's Mercy endureth forever.
So, pray, ask, obey, let God, and let go.