So that if Sprite1 is being dragged over Sprite2, then Sprite2 is also not dragged along with Sprite1.
You should have a variable to store which sprite is being dragged.
It is e.g. 0 when you aren't dragging, 1 when dragging Sprite1, ...
When you start dragging Sprite1 the value will become 1. You then move over Sprite2 and it must check if the variable is 2.
This is not the case so Sprite2 will not be moved.
I hope this makes any sense.