In the 1st act:
1. We need to convince Rolan to go with the refugees.
2. Don't let the Arch kill the goblin Sazz. (see achievement "She Cannot be Changed" 1 Act)
3. Save Mircon from the harpies.
4. Save Arabella (a Tiefling girl who was caught stealing)
5. After entering the grove, turn right, climb the mountain, and see how the goblin attacks Nadira, save her.
All this is done before you defend the emerald grove from the Minthara
6. All Tieflings are in the emerald grove, no one can be allowed to die
In the 2nd act
1. In the tavern "the last light" to learn from Tiefling Rolan that some Tieflings were caught and taken to prison, to rescue all Tieflings from prison
P.S.: Don't forget to walk around the tavern after the rescue and talk to the rescued Tieflings.
2. In the tavern "Last Light" do not let Isobel be kidnapped, otherwise everyone who was inside will die.
3. After the battle, find out from the children that Mol was kidnapped. (We will meet with the Pier in the 3rd act)
4. help Arabella find her parents (Arabella will be near the entrance to the "House of Healing" And the parents are inside)
5. Save Rolan, after our conversation he will go himself to save his friends, we will meet him near the river, below the central bridge that leads to the "Customs"
All this must be done before we go to look for the "Song of the Night"
6. After the battle with Keterik Torm, he will go after him, find the Tiefling Zevlor there and Save him, he will be closed in one of the capsules
In the 3rd act
1. To complete the quest "Save the Tieflings", we go and talk to Danis\Bexom, who is in a refugee camp.
2. If you decide not to give Lorroacan the Song of the Night, you must not allow Rolan to be killed.
3. Mot is in the Thieves Guild.
Achievement is given after completing the game.
Credit to HSePa on Steam Community Forums