A run out takes place when the batter who is running between the wickets fails to land the bat or a part of the body within the crease before the fielders dislodge the bails. A run out dismissal is not credited to the bowler.
One of the most commonly asked questions related to run outs is whether both batters can be run out on the same ball. According to the laws, the answer is No. The first batter who gets run out is the only one considered out. The ball becomes dead after this event.
A twisted version of this question is, can two wickets fall on the same delivery? The answer to this question is both yes and no. Let us understand this by an example.
Assume the batter misses a ball and the wicket-keeper fumbles while collecting the ball. The batters are in a dilemma whether to risk a run or not. Eventually, they do agree to run for it. The wicketkeeper though, collects the ball and hits the stumps. This results in one of the batters getting out, but the umpire signals a no ball as the bowler overstepped the crease before releasing the ball. As a thumb rule, the ball is not legal, but a run out is legal on a no ball. This means that the batter is out on a delivery that is not counted.
The next batter walks in. This batter gets out by any means like bowled, caught behind, etc on the very next ball, which is a fair delivery. Hence, this way if a no ball or wide accompanies a run out, followed by another dismissal on the next legal delivery, the batting team can lose two wickets in a single delivery. Moreover, should the legal delivery produce a run out, then it means that two run outs have taken place on the same ball.
Thus, on a single ball, legal or illegal, only one wicket can fall. But, on two different balls (one of which is illegal) two wickets can fall on each of them, eventually resulting in two wickets in one delivery.
