Need suggestions

[Antonella]

Two umpires system.
R1 on first base.
Release of the pitch and R1 goes for 2nd base attempting to steal.
Catcher’s throw goes to the outfield and R1 decides to stand up and continue her run towards 3rd base.
Again: defense’s throw goes over and the ball now is in foul territory, near the fence.
R1 goes on and try to get home plate. Finally defense make a valid play at home plate, with R1 sliding and defensive player tagging her, for a very close play.

I need help in order to know (according to the Systems used in USA or other) wich umpire is responsible for:
a) play on second base
b) play on third base
c) play at home plate

Every help will be greatly appreciated and much more if you can explain me WHY (good reasons) an umpire on THAT base is better than the other…

Ciao