For this achievement you must keep Salim alive and have good/okay relationships with the other protagonists. If you called in Air Support Salim will not have time to go find his son, so refuse Air Support as Eric at the start of the game.
It is also quite possible that if Merwin survives long enough to fix the radio Salim will not be able to return home to his son. To avoid this just kill off Merwin before
"The Signal".
Credit to ThePugHybrid for their
guide.