During Trinity Restored
So when I come to the Stone, Karliah is there but not Brynjolf. I enter the cave with Karliah, and Brynjolf magically appears through the cave entrance. That's fine. We run down to put on the armor, but as soon as Karliah says to put on the armor, Brynjolf turns around and leaves the cave. So I go the fire circle, and Karliah answers a question to Brynjolf, who isn't even there, and I can't continue, assuming because Brynjolf won't stay oin the Hall.

Any ways around this?

It seems like the lower glitch listed in the elder scrolls wikia but I've tried running into him and using Unrelenting Force and it barely moves him.

Actually I've finally pushed him into the final chamber - forgot about holding the button - and even onto his platform. But he just keep trying to leave. I can't summon noctural

Finally finished the quest. For those wh have this same glitch, here's what I did. I kept using Unrelenting Force and throwing his body ahead and then blocking him from leaving until the Shout restored. Finally I got him up to his platform in position with drawing my sword and small UF Shouts. Then I used Unrelenting Force at Karliah and knocked her into the water. Continued to block Brynjlf from leaving. As soon as Karliah headed back to the platform, when she stepped on the larger middle lower platform, I ran quickly to my side and Noctural appeared.

If you're having trouble also, try this and keep saving when you gain a lot of ground. Another player named Virtual Boy posted a guide like this I used at the trueachievement.com website. So props to him for the suggestions.

it sounds like you had another quest interfering with Brynolf where you probably would end up talking with him at a certain location, NPC's will head back to the locations your meant to talk to them at if they get teleported via another quest to a area.

I wonder if this technique would work if the two characters dont show up at the stone to begin with. I've managed to get Karliah out of the inn and following me a ways but didnt make it all the way to Riften.

sometimes the npc's will get stuck while walking to a area, and the only real fix i've found for that is to shout them to a road, sometimes they will backtrack the road first, then head to the location, but most the time once you get them to the road they start heading to the right area. Works great with Delphine and her getting stuck after leaving the peace meeting (just one example), careful of cliffs though, some npcs you'll kill if they go off a cliff even if they are needed for the quest.

I'm not sure what stops them both from showing up, but getting Karliah all the way there from shouting her there from the inn might be a major pain, but might work.