They Don’t Look Friendly – Rescued Kilmer’s bootleg character.
Who the Hell Are You Anyway? – Rescued Liza.
Both these achievements are obtained from rescuing npcs located in the same area. The area is hidden and only accessible once you jump a ramp.
The ramp entrance is located about halfway from Octopia to the River entrance as shown below.
The location is halfway between Octopia and the River. 
The ramp entrance is under the rock outcropping.
Once you through and jump the ramp, you’ll find a hidden location swarming with enemy troops. Wilmer will be located in a marked prison cell and Liza will be located in the crashed helicopter as shown below.
Once rescued, the achievement will unlock for each respective character.
Ducky Obrien 