You can tempt the hostiles in the main hall to follow you in small numbers down the stairs, where you can tackle them bit by bit without being swarmed under. You'll have to enter the hall to deal with the ones at the back, but don't under any circumstances go up the stairs on to the dais until all the enemy are down. When you've done that, retreat somewhere safe inside the Temple to heal. When that is done, dash up the steps to the secret door behind the altar, open it, and run along the passage until you get up on to one of the balconies. They can't get at you here, and you should be able to shoot down the majority of the skeletons that appear as soon as you go on to the dais. When you've cleared as many as you can, go back down towards the door behind the altar, and again tempt small numbers of the ones you haven't been able to reach to follow you so you can deal with them gradually.
It takes time, but it should be well doable at your level.
Incidentally, one of the torches in the passageway will bear closer examination! 
*hint*
