You may now only upgrade one non-status companion to C+ as indicated above and cannot upgrade more than one even if they are on the same PNR. However, I do not believe the one companion needs to be on the same PNR. This used to be true, but is not longer the case and they only require matching itin's. Note this text:

"You and a traveling companion may both enjoy a Complimentary Upgrade to Delta Comfort+® when traveling on Delta and certain Delta Connection carriers, as long as that companion is a SkyMiles Member, Medallion Member or partner airline elite member, and traveling on the same flight with matching itineraries."

I realize there is a later example which states the opposite, but I believe that this is simply a case of some example text not getting updated. This would now match FC companion upgrade policy which does not have a same PNR requirement. However, in both cases, companions on separate PNR's with no status will only be upgraded on day of departure after other Medallions have been upgraded.