Two Runners Occupying the Same Base

 
With no outs and the bases loaded, the batter has a 1-1 count. The next pitch is wild, the ball goes to the backstop, and the runner at 3rd base (R3) attempts to score. R3 gets in a rundown, but returns safely to 3rd base.
 
However, during the rundown the runner from second base (R2) advanced to 3rd base. The defense tags R3 and then R2 while both runners are standing on 3rd base.
 
Who is out and who is safe on this play? Did the defense need to tag the runners or is one (or both) called out because two runners are occupying the same base?  Does the order that the runners are tagged change the calls?
 
Is there an umpire mechanic that the umpire can use to reduce potential confusion about who is called "out" and who is called "safe"?
 
Call
A force play occurs when a runner loses his right to remain at his base when he is forced to the next base because the batter has become a batter-runner (NF 2-29-3).
 
In the situation below, R3 was not forced to home, so he may return to 3rd base if he desires. R2 was not forced to 3rd base on the passed ball, so if 3rd base is occupied, R2 must return to 2nd base or be at risk of being tagged out. So in the situation below, R3 is safe and R2 is out. The order that these runners are tagged does not change the calls.
 
The base umpire should point to R3 and call him "safe" and point to R2 and call him out.