Elephants move at their move range - no dice rolls.
An Elephant standing on a Gladiator, will move toward its next target and trample them if it is within range (2 hexes away). If no other Gladiators are that close, the Elephant will move off the unit it is currently trampling and stay adjacent to it.
They WILL Trample on consecutive turns if other targets are in range!
While Trample is an innate skill that happens on the Move Phase, because the Elephant is on top of the Champion/Gladiator, no attack happens (other than the Trample damage of 1 and the Stun). The only exception to this is Hannibal Barca.
It IS possible for Hannibal Barca to Trample your Champion and then attack one of your other gladiators if they are in range. This is because of Champion Bound (Innate).
While standing on the Champion, it is considered "not in range," and therefore Barca will set his eyes on the next target that IS in range. On Barca's next turn, it will move off of your Champion (as per the Trample rule), but will always stay next to your Champion because of Champion Bound.
Therefore, the ONLY way Barca could use Trample two turns in a row is if one of your Gladiators was standing in the way of the most direct route to your Champion.