To answer your questions:

1) If your airplane is far away from you, and someone turns on a transmiter closer to the airplane than you, the stronger signal wins.

2) If two transmiters have full range over the same airplane, it will react totally erratic, according to control inputs on each transmiter.

3) About 2 miles.

In real life, things vary, I remember I was flying a twin airplane on a fun fly event, when someone (outside of the flying field) wanted to have fun in his own way, and turned on a powerful transmiter signal, my airplane went full throttle in a vertical dive from about 200 feet, my inputs were totally nulled. (12 other aircraft were destroyed by this genious on that Sunday).

On a Sunday morning I was flying my 1/4 scale Decathlon, when someone turned the same frequency to check his radio, I was flying at about 100 feet high, the airplane went on a dive of about 30 deg., I had no control whatsoever.

I've had other hits, were my airplane went completely crazy, totally without control and doing loops and rolls and snaps and you name it, and then all of a sudden, full control again.

Today's radios are much better and less problems occurr .