You need to pull all of the levers in the correct order to open the room under the rock and safely remove the statue. If you have a recent save before pulling the first lever out of order, you can reload it. If not, you are only missing a bit of loot.
You do not have to defeat the last gargoyle and earth elemental. If you have one character pull the last lever, the other can remain in the central room, and run up the stairs after the statue comes alive and moves out of the way.
If you want to defeat them, you can have one character use a bow/crossbow or magic (though the more powerful spells are not available until act 2) while the other character either runs around distracting them or uses hit and run tactics, allowing the first to do most of the damage from a distance.