We often find ourselves helping a relative or friend for the thousandth time with the same old issue. Whether it be financial, social, or helping with some addiction the issue comes up again and again.
The trick with this isn't helping, it's letting go. You can't MAKE someone behave when they're bent on misbehaving. They'll do what they want to do, all you can do is offer them suggestions and let life take it's course.

Once you accept this for what it is - out of your control - you'll sleep easier and you'll live longer by not trying to make silk purses out of sow's ears. You need to suggest that they behave. If they come to you asking for advice give it to them. Then let go. If they ask again give it again. Don't loan them money (Never loan money to family or friends! Ever!) and don't offer them more than they need. They're on their downward spiral and they'll drag you down with them if you don't let them go. Once they hit rock bottom they'll decide they need to make some major changes in their lives and they wont NEED your help.

Take a step back and just let them go.