if you have a license you can try placing the 4 objects into a family, and compare (I don't know what) the clicked object with the family.
If you don't, try using 2 global variables.. set them when the objects appear/are created, one per object.
Since I don't know what you are trying to compare, or what to do next I can't give you a practical answer...
You can also use the "pick all"condition and referece the 4 objects, then check the variable