We had an informal intervention about 3 years ago for my now ex husband. I read this book...Love First: A New Approach to Intervention for Alcoholism and Drug Addiction. It was very helpful and will help guide you to how many people/who should be involved, how to write an impact letter, where to hold one, etc., if you decide not to use a professional.
In my opinion, regardless of what route you take...private or professional, you need to be prepared to do what is asked of you after the intervention if they don't go and that is to stop enabling. Cut off contact and make sure there are consequences. If you aren't ready to do that then you'll not get the outcome you seek. We, as enablers have to be ready to make a change as much as the alcoholic has to be ready to make a change or we're no closer to recovery than we were when we started.
Hosting an intervention is very scary and emotional but you're doing it because you love him and you want to save his life. Just remember that. Best of luck to you and your family.