I ran into this as well (Malady and Gareth acting as if they are in a fight, unable to talk with them) and we fixed it by attacking Gareth with a single character. When the character dies they are ported out and Malady and Gareth reset, and we were able to talk to them.
The character we used to attack them lost enough attitude where they wouldn't speak to him, but the other party members could trigger the ending just fine.
If anyone's stuck at the same spot and are wondering if it's worth loading the game up to play the rest, it's literally just a handful of lines of dialogue and another clip of the boat traversing the map before it kicks you to the main menu.
If you have a rogue that can sneak decently you can hide and launch a single attack while the rest of your party members are away, and then they will be out of combat, and go to their intended positions.
