On separate PNRs, it’s possible to ask the airline to add a “TCP note” (to complete party, referencing the other passengers) in the “OSI field” (other services information). This has to be read by the agent, which makes it less than reliable, but it can be very useful during IROPS ((irregular operations) when there might be a cancellation or / and involuntary rerouting to keep everyone together.

This possibility isn’t particular to TP; it’s standard operating procedure on all, or nearly all, automated airline passenger service systems.