This mission can be started at X: 441.0, Y: 327.4 , from an injured man inside of a building. He says that three men with guns attacked him and killed his family, and he wants revenge. Go outside and make your way to the first marker, which is where the first privateer is located. There is a Heavy and two men with SMGs guarding him, so take them all out and kill the target.
The second privateer is located north from the first one. He is sitting on a boat, with a sniper and two normal enemies on land, as well as a guy with a RPG next to him on the boat. The third guy is north of the second, and is guarded by two guys with SMGs, as well as two normal enemies. Once all three are dead, head back to the initial guy who gave you the mission to finish it, with your reward being $500.