This is what it says, but if one person in your party drinks and another doesn't, as is the case with us (DW doesn't drink, I do), you can call Celebrity and request that the non-drinking person be allowed to purchase the less expensive (non-alcohol) package instead of the alcohol package, and they will arrange it for you.
For our next sailing on Summit, I have the premium alcohol package, and DW has the basic non- alcohol package. It only took one simple phone call to customer service to set it up, and they were very accommodating. But you do have to make the phone call, as it's not advertised they will do this, because of course they're counting on you not to be aware of this, and to just buy the alcohol package for both persons (as the rules read).
Saved us over $400 for our sailing..