Random Waypoints

Start with placing down how ever many markers you need on the map. Place them in the areas you want the group to have a chance of going to. Then start changing the names of the markers. Now name the leader of the group something. It can be anything. If the entire group is in a vehicle name the vehicle.

Now create a trigger. Place it wherever has empty space. Now edit the trigger's attributes to make the Activation = Any Player and the Activation Type = Not Present.

Then add this to the On Activation field of the trigger:

nameGroup= group PLACEHOLDER1; 
randomPoint= selectRandom ["PLACEHOLDER2", "PLACEHOLDER3", "PLACEHOLDER4", "PLACEHOLDER5"]; 
 
_wp = nameGroup addWaypoint [getMarkerPos "randomPoint", 0]; 
_wp setWaypointType "MOVE"; 
_wp setWaypointSpeed "NORMAL"; 
_wp showWaypoint "NEVER";
_wp setWPPos markerPos randomPoint;

Replace the first placeholder with whatever you named the group's leader / vehicle. Then start replacing the rest of the placeholders with whatever names you gave your markers.

[ARMA 3] Random Waypoints by u/Pastlactose3213141