If you're going to get technical, companion is the correct word because even though friendship is implied in its use, companions don't have to be friends, they just have to spend a lot of time together or be travelling together, which fits the bill here. Also companion doesn't imply hierarchy, it's a neutral term in that sense. And furthermore the word companion is used because it's common shorthand in RPGs for characters that form members of your party in a game.
I know what companions means, but players don't see it like that. Most players see them as followers (they lead, the rest follow), not companions. Especially not companions of circumstance that might leave them once that circumstance is resolved.
