To answer the questions in your first post, deathtouched darts don't work on Zamorak himself, but they do work on the other enemies in the dungeon - however, one of the minibosses, the one who self-heals, can withstand multiple darts before dying. He isn't entirely immune to them, though, just partially.
As to the second post, IIRC there are two situations where you might be unable to activate the next edict - one is if you haven't done enough damage to Zamorak to reach the next checkpoint, in which case just keep damaging him until it eventually triggers, while the other is if the flow of energy to the edicts is being interrupted, in which case you need to manually go back into Infernus and kill the witch channeler there, then return to the battlefield.
I think what you're describing is probably the latter situation, but I can't 100% guarantee I'm not forgetting something. I tried checking the wiki, but I guess the Zamorak fight is still too recent for it to include all the details.
05-Aug-2022 07:11:23