3 man crew

Lots of people disagree on this but here is my take. In this case it would be easiest for the third base umpire to take the ball and have U1 and UIC revert to the two man mechanics.

It doesn't say in the OP but I'm assuming no runners. In baseball, this is the U3's call. He has F8 straight up and going back. He also has all calls in left field. The U1 has F8 coming in and all calls in right field. The PU has no outfield coverage at all.
On the ball bouncing over the fence the U3 should go out, U1 rotates in and the PU comes up to cover third.
Once U3 kills the ball on the double the PU makes the award. The U1 should stay out of it completely unless there is a conference.

My apologies MST but there was a runner on second when the ball was hit.

Sorry for the leaving that out.

OK, this makes a difference. Before the play, U1 will be in deep B. U3 will be on the wing in D. When the ball is hit to left center, U1 has the V so it will probably be his call. He may slide and watch the catch or go out to get a better look. If he goes out the U3 goes in to take the runners. Once the U1 signals the ball out of play then PU makes the awards.
The interesting part is what happens if U3 had been inside. Any combination of runners with a R1. U3 is in C. U1 is on the wing in A. When the ball is hit to left center the U3 has a choice. He may slide over and watch the play from the infield or he may go out and get a better look. The U1 would rotate in and take the BR to second. PU stays home.
Any way you slice it it's the ump's in the middle call and the other two are out of it. The only time it's different is with either are inside the remaining wing has the fielder to the line and PU has the other wing fielder to the line.