Heres a question..

There are a few things missing, but let me tell you what happens here.

In the pregame conference we instruct both coaches that if a ball should go under the fence, the outfielder should throw up his hands and DO NOT make an effort to reach under the fence for the ball. The runners are to keep running and at the conclusion of the play the base umpire will go out and confirm the ball is out of play. If it is out of play then the UIC will return baserunners to the position they belong.

In your post it is unclear whether or not the outfielder left the ball under the fence or attempted to get it. If he reached under the fence and made an attempt at a play, then its all the runners can get.

If the player left the ball under the fence and the umpire goes out and sees the ball under the fence, he would have no choice but to rule a book rule double.

So it depends on what your brothers teammate did. It could have been the right call, or a bad call.......and by the way, there is no such thing as "redo the play".

Its either book rule double with runners on 2nd and 3rd or HR.