Wait for the students NPCs to enter the cave and walk to the meditation mats one by one. After all three have entered and sat down, a spider will spawn. WAIT until Galabo reacts to the spider, then right click and "shoo" it. If you were patient and did not shoo the spider too soon, you will receive a notification 'You hear someone entering the cave' and Pacificator Merrek will soon join the group. If you were impatient and did not wait for Galabo to react, Merrek will not enter and you will have to zone out and start over.
Listen to the dialogue between Pacificator Merrek and the students.