[quote=@Bright_Ops]
[@Conscripts]

Okay... I'm going to raise two points for you to answer before the Gm says anything one way or another. 

1: How effective do you truly believe war elephants are going to be in a mountain pass?

2: How do you expect to feed and look after the elephants as the campaign drags on? After all, this isn't just going to be a single battle, but a drawn out engagement that we are on the defensive of.
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If you are going to send a bunch of men in there, you'll need plenty of food. The elephants are big creatures, and can carry tons on his back. So there should be no reason they cannot carry provisions into the camp on its back. You can have a castle on it. 

And its effectiveness, I believe that in a mountain pass, elephants can sometimes even more effective than horses. If you are in a steep pass, like the battle of Thermopylae, then I think we should not send mounted soldiers at all, since it is very narrow and not effective for cavalry uses. If in the slightly open field, with hills on both sides, you can also use the elephants to your advantage, to block the enemy's advances. It might not be able to commit a charge of its own, but it can stop enemy charges and be a defensive wall. It gives soldiers on top of it high flatform to shoot arrows from it. In the end, I believe that mountain passes aren't cavalries home, but you can still use it to your advantage.

EDIT: Also, if an elephant freaks out during the attack and runs away, there is a slight chance that it will rush towards the front, trampling the enemy. But still, it's all bound to the animal itself, as it does not distinguish allies or foes then. 

But still, the choice is up to the GM. I will consider the numbers, since 50 is a bit too many to squeeze into a mountain pass. I might only go around 10-20 of them. But if it does not fit with the GM either, then I'll just switch to plain cavalry.