Fugitives - The Farmstead
Upon reaching the farm, choose either option to get rid of the old people. Now, go to the main room and have both players go to the grandfather clock underneath the stairs. Both players have to interact (X) with it at the same time even though there is no prompt. This will open a secret door on the stair case. Go instead the secret room and interact with the treasure chest. Achievement unlocks.
This achievement can be seen in the video guide at 6:44:NOTE:
Achievements are only available to owners of the game. Players using the "Free Trial" friend pass will NOT unlock achievements.