Two runners on third base

[Guest Mark]

Runner on third base.  A runner on second base steals third on the pitch.  Both runner now standing on third.  Who’s out? And can the runner that stole  third go back to second once he stepped on the third base bag.

[mark38090]

Depends on who was tagged if anyone was tagged. The lead runner owns the bag so he is fresher while on the bag it's nothing. If the trail runner is tagged he would be out. If the trailing runner isn't tagged and retreats back to second safely then he's fine. 

[maven]

The TOP runner is entitled to the base when more than 1 runner arrives there, unless he's forced to advance (and in that case the trailing runner is entitled to it).

Remember that this "entitlement" applies only when more than 1 runner is touching a base. Otherwise, a base is safe haven for a runner (from being tagged out) unless he's forced to advance.

[The Man in Blue]

*TOP runner meaning the runner on the bag at the "time of pitch" (not some reference to position).