Just my opinion, but I have the feeling his entire family knows what has been going on. They just behave as if they're in the dark. If you don't send the email to your AH's parents, they'll get it from one of the recipients.
From my own personal experience, I have discovered that a family closes ranks and goes into denial overdrive when anyone tries to come in and upset the balance of their system - even their extremely dysfunctional system. My AH went on a three-week bender last October. He was hospitalized three times. I honestly thought he was going to die that time 'round. So I called his two brothers and his sister. I thought they should know how bad their brother was in case he died during that time. I didn't want to blindside them with, "Your brother just dropped dead." I believed I was preparing them for the worst.
My former counselor, whose speciality is addictions counseling, called my AH's oldest brother who is a psychologist who works with addicted kids. Outcome: AH's two oldest brothers made one phone call a piece to express their "concern" for their younger brother. My sister-in-law just stuck her head in the sand, and after that it was not their problem any longer.
The results are my AH is still a drunk; his family knows he's a drunk and minds their own business, and as far as I'm concerned .... well, what they think of me is none of my business.
They'll think what they want to regardless of what I say to them.
You want them to hear your side of the story. Do you think it will make your AH get sober? Do you think they can make him get sober? The reality is, that only the addict can make the decision to get sober. Sad and tragic, but true.