I entered the cave with the unconscious Findal from the grove side, and snuck up fairly close with my party (4 custom characters).
Once the fight started, there were some odd issues. I got a surprise round, all my party members were in the fight, and many of them had similar initiative, where they should have been able to act at about the same time. They had the "intertwined portrait" thing. And yet, I couldn't select the other members next to me, either clicking on their portraits, or in the "End Turn" screen, which only showed the one character of mine. Clicking end turn did NOT get those members to go, instead, it quickly wrapped around to the first character again, who initiated the attack.
It's as if MY party was also surprised, even though the fight was initiated by me, and they were right there nearby.