All right, you can change the position of your markers by using the following command :
mymarker setmarkerpos "format position", where format position looks like this : [x,y,z] (in the case of markers, z is optional) or like this : getpos myobject.
Put the markers somewhere on the map (to know how to hide or show them, there is a Tut ; you need to have an init.sqs file where you write "mymarker" setmarkertype "empty", etc.)
As it is your first script, I suggest that you use invisible Game Logic objects. In which case, your script will be :
_nade="grenade" camcreate getpos gamelogic1 etc;
And to change their positions :
gamelogic1 setpos [x,y,z]