You can use instance variables as conditions for picking... for example you can have the one you are dragging with an instance variable that is called IsBeingDragged and use it like a boolean value (on or off - 0 or 1).
Then you can use this variable as part of your picking comparison (if sprite.variable(IsBeingDragged)=1)
Likewise you can apply instance variables to the pawns still on the board based on whatever criteria you choose (a positioning number, or a unique count/ID, etc) as the other half of the picking condition.
As
davidochoa mentioned, you can try to use containers for easier picking - just be aware that if you are destorying any object in the container it will also destroy other members of the container. You can set these items to invisible instead of destroying them as an alternative way (this is how I have limb dismemberment working on my container based character model).
Hope this helps
*EDIT*
Looking at your newly included code screen capture, you can also simply try adding a loop "for each yellow" into your event condition in row 34. I think that should work.
~Sol