Can both batsmen at the crease have a runner each?

What is a runner?

Runner is a player who runs between the wicket for an injured batsman of his team. When a Runner is in play, the injured batsman for whom he had been deployed, the batsman normally stands in his crease and plays shots but doesn't run between the wickets. The Runner runs for him. When the batsman is in strike for which the runner is on the field, the runner takes up his position at distance away from the pitch of play depending upon the umpire's dicretion, normally on a pitch which is parallel to the pitch on which the game is being played.

When the injured batsman is off strike, he goes and stands beside the square leg umpire and his runner stands in the other end of the pitch from which the bowler is bowling.

When can a runner be used?

A runner could be used when the batsman at the crease is either ill or injured. The use of a runner by the batting team must be approved by the on-field umpires and it is a must that the runner is part of the playing 11 of the team, the twelfth man cannot be used a runner. Ideally, a batsman who have already batted in the innings is used as a runner, if possible and he might wear all the external protective equipments that a batsman should wear and it is a must for the runner to carry a bat with him.

If either the batsman who had been injured and his runner is out of their and the batsman is liable to be stumped out or run out and the runner, just like the batsman is subjected to rules of handling the ball and obstructing the field and in either of the cases if the runner is found to be guilty, the batsman for whom he is performing his duties, is declared out.

Can both batsmen at the crease have a runner each?

Yes they can, provided the fielding side doesn't oppose but the rules had been changed and the discretion of allowing the batting side to have a runner is solely depends upon the umpires. Previously, the batsman was only allowed a runner if he got injured during the match, but now a batsman suffering from cramps is also allowed to have runners

Example:

The incident of two batsmen each having a runner in an international cricket match happened in 2003 during Australia's tour of West Indies, in the 4th test match of the series in Guyana when Shivnarine Chanderpaul and wicket-keeper batsman Ridley Jacobs both had runners in Wevell Hinds and Marlon Samuels.

In 2011, the International Cricket Council had announced that commencing from October 2011, runners would no longer be used in international crikcet.