Spears as stack defense, try to hug defensive terrain. Fortunately jumbos don't flank damage your siege.
Then, when attacking cities, elephants are pretty terrible vs CR siege, because they don't get defensive bonuses. A CR II catapult or any kind of treb will own them silly, especially after a round of collateral (and the elephant won't come up as a 1st defender, meaning when they're in cities they're doing very little to you or your siege).
The alternative is to kill them or take away their ivory before construction/hbr.