Runner Interference on IFF Rule

OBR. R1 and R2 with no outs. B3 hits routine pop-up to F3. However, R1 unintentionally interfers with F3 and precludes his ability to get to the ball with ordinary effort. Ball lands in fair territory, then is finally touched in foul territory. What do we have? Would the result change if the ball WAS touched in fair territory? Does the IFF rule come into play, or does the interference kill the ball immediately and superceded the IFF rule? Very strange one. The call made after the BU and PU conferred was B3 out and R1 back to 1B. I know this was wrong since R1 has to be out and play is dead immediately upon the call of interference. So question is, should B3 be out as well.

Leo