The Monolith survivors is a side mission given by Strider in Call of Pripyat
Stider, a leader of a Monolith squad, recently regained their freedom from the Monolith and seeks shelter before they are found by other stalkers due to them wearing Monolith uniforms.
You can find Strider just north of the container warehouses and near the bridge going to the AA complex in Yanov. They are off the road and can be found easily on radar.
You can recruit Strider and his squad into either Freedom or Duty by talking to Loki and Shulga respectively. However one will need to earn the trust of one of the leaders for them to send recruiters.
Generally, giving either leader Morgan's PDA or General Tachenko's PDA will be enough to trust you. Anything less won't be enough.
Strider and his squad taking the Duty oath.
Strider and his squad being debriefed about Freedom's ways and ideals.