The problem with this system is that if you play as a 4 player coop team, you can NEVER bring any of the Origin companions with you, and therefore you can never finish their quests the way you want to.
Example:
if you cannot bring Shadowheart to
the Shadowfell, you can't free the Nightsong without Shadowheart leaving your party.
A custom party of 4 should be able to leave one Tav at the camp and then assign Shadowheart to the player whose Tav is currently waiting. It's an easy solution and this feature should frankly be mandatory. In fact, it''s super immersion-breaking to not have this option.