for what its worth....and in my opinon only, I believe most interventions that arent successful is due to the family members who cave in, back down onthier boundaries. They cant stand to see the alcoholic get angry and they give in to doing things his/her way....thas why a professional interventionist is needed. To manage the backbone of the family members.
Unless that family member is a black belt alanon, the success rate is very diminished.
Seek a pro...google "Interventionists", they are everywhere. good luck!!