You can just have them hold position, I've had no problems in preventing the party from running into the aoe. The fight still drags on in rtwp, even if it's over faster, because of the waves of teleporting enemies.
Which is another annoying mechanics. Enemies spawning is such a slow animation, what happens often in my game is that the model is already there and there are red-circled, but my party cannot target them.
Party members use to ignore the hold position, even more if you have a staff and a cantrip in autocast, they sometimes go into melee just for the kicks, I assume, but yeah, there are ways to do that, but that´s more of a personal preference. As I said before, you can play that fight even in core and above in real time, I just do not have much fun playing like that.
