I'm doing Zerith-Var's first quest, currently exploring the small cave on Khenarthis Roost underneath what's left of the temple of the twin moons.
With me is another player, we are not grouped. With them is another copy of Zerith-Var, which I can interact with.
After interacting with the piece of the broken alter, I can start the dialogue option with
their Zerith-Var.
Boy, I hope that's not going to lead to any complications further down the road.
Picture 1: Unknown player and their Zerith-Var, wearing the light armor set, to the left. Me and my companion to the right.

Picture 2: Me, entering the dialogue window with all options accessible atfer interacting with
their Zerith-Var