I think that the general Centurion lounge policy is one drink at a time but some lounges are much stricter than others and SFO is the one that seems strictest; others not so much. If you look at a few of the specific lounge threads you will see discussion of this over the years. Here are a couple of posts that have discussion following the linked post of 1 drink 1 person:
https://www.flyertalk.com/forum/31840975-post1296.html (lots of discussion in this thread over the years)
https://www.flyertalk.com/forum/30690613-post853.html