Just to add a data point. My wife (silver) and I (plat.) are traveling on one reservation (both booked into E+)

We have 2 friends traveling with us neither have status.

Friend #1 on a RT tix purchased through UA
Friend #2 on award ticket outbound using my wife's miles to buy his ticket and returning on an award ticket with my miles

Website allows: Outbound me & wife in E+, friend #1 & #2 in E-

First call to UA was told: wife is my companion,
-friend #2 can sit in E+ on return (since their tix was using my miles)
-both friends sit in E- on outbound.
-When we check in wife is counted as having E+ access and we can each bring one friend up to E+ with us no charge if there is space

Second call to UA: All four of us sitting E+ for entire trip. No problem, not even a hesitation.

So... YMMV...