Okay, I'll take a long-shot at this.
Since both runners passed the commitment line, and since the second home plate replaces the "tagging" of the runner, I vote for #1, double play. My thinking (huh?) is that this would be the equivalent to two runners coming in to home plate and the catcher tags both runners prior to either of them touching home plate.
Now Mike, I'm hoping that since you only gave us 4 choices, the answer is one of them and not a 5th choice that you left out.
Or is the 5th choice R2 not only "caught up" with R1, but also passed him?
Serg