i think its quite easy especially if everyone's names are different.

add 1st companion at check in and add the second at the gate or PC. i may be incorrect but i believe that once the companion is added, there is really no easily viewed way to reference the elite passenger.

i added my mom and then my brother in phx and they were both called at two different times once the list was cleared.

i will admit though, that i have only tired this once. im 1 for 1. good luck even getting an open seat for yourself, much less a companion.