As the now ex of an alcoholic. If he went through a treatment plan and got himself together and then I sat down for a meal with him and he ordered a beer, I would be thinking "Oh s**t, here we go ahead." I would expect him to tell me how he is a casual drinker now and the last decade of my life was just a rough patch he was going through.
I say that to say this, I can understand your concern. You don't want to see the look on their faces when they find out you've been casually drinking. The year 2007 wasn't exactly the dark ages. I'm sure the DUI and the ensuing jail time, their embarrassment, and their hurt (which are their feelings and their issue of course but from their perspective mind you) are all still near the surface.
I would find it more believable that you have learned to moderate your alcohol and can be in a celebratory situation without going overboard if you brought the subject up in the context of wedding plans. Tell your family you are planning to have alcohol at the wedding, that you are planning a champagne toast, and that you have learned to moderate so you don't see any threat to your sobriety. Then...show them that you can have a glass of wine when out at dinner and walk away.
Actions will always speak louder than words for family. Alcoholics talk the talk but can't always follow through. Show your family between now and December that 2007 was just a rough patch for you and that things are different now. By the time the wedding rolls around, they will be at ease seeing you raise your glass to a toast and there won't be an elephant in the room when you do it.
Congratulations on your engagement!!
Alice