Both of these achievements are unlocked in the same location by rescuing Wilmer and Liza from a hidden facility. The facility can only be accessed via a hidden ramp located about halfway between Octopia and the River entrance as shown below.


The ramp is located under a rock outcropping as shown below:


Once you jump the ramp and clear the hidden facility of enemies, Wilmer will be located in the marked prison cell and Liza will be located in the unmarked crashed helicopter as shown below:


Once you rescue the two prisoners, you will unlock their respective achievements.