I’m sorry, but even if your companions on other PNRs had been eligible for MCE, PNRs are not capable of being “linked” in any meaningful way. “Linking” is actually an addition of a “TCP” (To Complete Party) note in the “OSI” (Other Service Information) field in each PNR. When that is done, it still requires a human open Zander read the OSI field in the PNR. “Linking” works better, but not always, in IROPS and flight cancellations and reaccommodations than in keeping the same seats.

See FAQ: TCP, "Linking" / link / merge itineraries / PNR (master thread)