"I will go first, just in case something is wrong on the other side. It would be convenient if we could see the other side of this portal, but it appears to be totally black, so they might have blocked their side as well. I can deal with that, but don't follow until I signal that it is safe to come through." Cain informed the others.
He merged with Oath Breaker, whose teleportation ability was excellent for this purpose and would let him easily return to where he started if the far side was blocked so that he wouldn't get squashed against whatever was blocking the exit.
The guard lifted the stone for them to exit through the portal, and Cain stepped through, leading the way in case there was something unexpected on the other side. The portal was heavily guarded at this end, so there was no reason to believe it wouldn't be guarded on the other side.