The painting puzzle?

[Grandork]

The NPC says to adjust 3 of them, which I did, but didn't work. Does the order matter?

[K.I.L.E.R]

Go back to base and purchase a skill with mana, it allows you to see magical threads not visible normally to the naked eye.

Destroy treasure via alchemy to make up the mana in order to buy the skill.

[Landale]

You need Shine Light to reveal the 3rd one that needs to be interacted with. From the guide:

Head back to the room with Gartan and activate Shine Light. Check the top picture on the west wall, then the middle picture on the east wall, then finally the picture on the opposite side of the wall from the Gartan. You can't see it nor interact with it without Shine Light, so make sure it's on. Go to the locked door event again and it should open. Talk to Gartan again and he'll leave.