The enemies ignored both of them. Allegedly, anyway. I know when I played The Last of Us at launch, there were times that enemies saw me when I thought I was perfectly hidden while Ellie was out in the middle of no man's land. In both cases, the enemy AI ignored these other characters because A) escort missions have never been fun, and B) it slowly builds a reason for you, the player, to grow attached to these characters when they help you. You feel the resource deficit in Infinite when Ellie's not there to throw them to you. Both games did basically come up with the same gimmick in the same year.