You can do Halls of Stone with four people.
Okay, we had five, but one was a bot. The Healer picked him out after the first couple of trash pulls. "Why is a Warrior with 5200 GS only doing 1000 DPS?" he asked in party chat. Then, when I went to go tell Bran to get a move on, I suddenly realized I had a shadow.
"He's on follow for you," the Healer whispered me.
Unfortunately, we couldn't kick him at the time because we had the "protect Bran" event going on.
"No heals for the bot!" the call went out.
Amazingly enough, the bot died second. We lost the Lock first, and then the bot.
For the last two minutes of the event, it was just the tank, myself, and the healer trying to keep threat off of Bran and keep ourselves upright. Kudos to the Tree who did the job.
We kicked the bot -it was set to Need everything too- and then we finished up with the last boss.