If you are aiming for Savior of Skara Brae, this trophy is missable.
Is attainable on one run, but PAY ATTENTION to your save files.
You are only allowed 20 saves per game. If you go over that many, saves will start to get OVERWRITTEN
To prevent this be sure to LOCK your save with triangle button on PS4 or PS5.
After beating Tarjan and going back to Rabbie in Skara Brae Below. A sister will appear behind Rabbie to start The Blessed Lady Quest. SAVE BEFORE going to Skara Brae Above. Once Above you cannot return to the adventurer's guild to swap out party members. Locking you out of this achievement or Savior of Skara Brae.
Pick only 3 party members. Save your game and then LOCK your save BEFORE speaking to Rabbie after The Blood of Kings quest. to AVOID a complete second run through of the game.
Once this achievement pops then you may reload your locked save to change your party members to 6 members and proceed to the final dungeon again to beat the boss again to get Savior of Skara Brae and avoid a full run through of the game a second time.