If you are an A-lLst member and book multiple tickets in the same transaction, everyone in the party gets sequential boarding positions. You don't need companion status, but you do need to book multiple tickets in the same reservation. Companion passes are booked together so that meets the criteria. Without a companion pass, you cannot book the member ticket and then purchase another ticket for the same flight and get sequential boarding pass numbers.
How can you tell if the tickets were booked together? Every reservation has its own code but when you bring up your confirmation code, you will see the other reservations on the same page if they were booked together.
If someone in the party books or adds on an upgraded boarding position, the rest of the party is not upgraded. That would break the boarding position sequence. If the A-Lister purchases a business select ticket (companion pass or not), their boarding party will not receive a sequential business select boarding pass.
The one rule I don't agree with is what happens if you (and companion or party) are rebooked on another flight and end up with C boarding positions. As an A-Lister, you can board between A and B groups, but your companion (or other parties in same reservation) do not get to board with you between A and B groups unless they also have A-List status.
