Is it possible to dismiss both the batsmen in ground(ie,by a catch and a run out)?
No. It is not possible to dismiss both batsmen on the same delivery. Only one batsman can be legally dismissed. In the event of both being dismissed on the same delivery, the batsman dismissed first goes back to the pavilion while the other continues with his/her innings.
Is "Hit the ball twice" out?
According to the Laws of Cricket (Law 34 - as stated below), if done intentionally, then yes, it is out.
Law 34 (Hit the ball twice)
1. Out Hit the ball twice
The striker is out Hit the ball twice if, while the ball is in play, it strikes any part of his person or is struck by his bat and, before the ball has been touched by a fielder, he willfully strikes it again with his bat or person, other than a hand not holding the bat, except for the sole purpose of guarding his wicket. See 3 below and Laws 33 (Handled the ball) and 37 (Obstructing the field)....