Randomizer, you're a lifesaver. Thank you.
For anyone in the future who finds this thread looking for solutions to the beam puzzle:
In the first room with the mirrors and beams, set up the mirrors in the /\/\ pattern that Randomizer mentioned, with the mirror furthest to the right sitting on top of one of the runes. Step on the rune above that last mirror and watch the beams kill each other. Then push the last mirror up against the far wall - so the layout is now /\/_\, with _ being a one-tile space - which will direct a beam into the last beam emitter, and you can then walk up the passage and continue.
When you reach the second beam room, you only have two mirrors, and the beams are pointing south instead of north. This time, use the mirrors like this: \/. Set them up in that arrangement each time, pointing at a new emitter, then walk south to trigger the runes. Work your way along the room in this fashion, breaking each crystal as you go. Because the room is so long, your party should fit safely behind the mirrors each time.