Dead Rising 3

To unlock this achievement, you will need the third tier upgrade in Mechanic (called Man Magnet) which requires 6 attribute points, and the third tier upgrade in Smarts (called Mean Girls) which requires 4. Both of these upgrades increase your maximum posse size and are needed for the achievement.

The second prerequisite for this achievement is to have 5 survivors at the Survivor Bulletin Board. Survivors are gained by completing side quests (you can check if you will receive a survivor as a reward for a mission in the Map & Missions tab). The earliest you should be able to have enough survivors is in chapter 3.

Once you have both of the upgrades and 5 survivors at the bulletin board, simply go to a Safe Zone and select all 5 survivors. They should all appear around you and the achievement should pop shortly after.

On Instinct's solution tells you everything about unlocking this achievement but I wanted to warn you about something: this achievement is kind of "missable" (not really, tho).

/!\ when you end the story you won't have any survivor left at the Survivor Bulletin Board when you select another chapter or start a new run /!\
That means you must do this achievement around the sixth chapter or before (which is absolutely not hard as long as you have completed some side missions).

If you didn't unlock this achievement during your story run because you thought you would be able to unlock it during chapter select (as I did), one of the fastest way to gather 5 survivors is to start from Chapter 2 in Chapter Select and do these side missions:

Chapter 2:
-Craven Consultant (find cleaver + chainsaw)
-In The Cards (find 5 cards marked on the map)
-Darker Gods (the woman in the graveyard. When you have destroyed every sigil, go back and talk to the woman and HIT HER WITH YOUR HANDS before she kills herself with a knife, otherwise she won't be available as a survivor)

That's 3 survivors already. Now you have to follow the main mission until you get to Chapter 3.
During this chapter you'll receive the quest called "Blood Barter" when you are on your way to the police station. It's a very quick mission, you'll simply have to fight two guys. Be careful: don't kill the NPC called Jesse (the bodyguard) otherwise he won't be available as a survivor. Now end the quest and BOOM you got +2 survivors which means you have 5 now so you can use the board to claim your achievement.

Two last things:
-Tier 6 of the Life attributes is "Survivor Recovery". If you get this, your survivors will never get killed (they just go back to the safehouse if they've lost too much health).
-When a survivor is following you, enter in a vehicle and drive as far as you can from him: he will automatically go back to the safehouse.

Just two tips so that you don't bother going back to the safehouse to "recall" your survivors because you're afraid they get killed. It saves some time.