So reporting back - I think United may have fixed the mess created for splitting.

3 pax RT itin, I'm the only elite. When I checked in online for first flight, it asked which companion I wished to designate as my "companion". Reservation split into 3 PNRs. My designated companion appeared on upgrade list right below me. However, all three passengers had BG 1.

On return, my designated companion *also* appeared right next to me on UG list, and all three of us had BG1 status. In addition, I was able to switch E+ seats for my other companion without getting a charge for it, which used to be the case.

So, it seems that UA properly allows all pax on the original PNR to retain the elite benefits "inherited" from the status passenger, and only limits the CPU benefit to one pax. This is a very positive step if others can verify it.