unfortunately, they do require the room balance to be paid at check in...
however, i know exactly how you feel, as i have gone many times with other family members. they can divide the total amount amongst how ever many people you have that are paying. for instance when i went we had 2 rooms, but were being divided up in to 3, for our 3 different parties.
what the other user meant about leaving a card on file was that they'll ask you if you would like to have your room cards to be chargeable to your room. they will have specific names and numbers on them. so, you can purchase things with the cards and have it charged to your room. we always do this. there is no extra charge to do this. it is just more secure. if you lose your room card, or it gets stolen, they can cancel that number, and then issue a new one to you. this way, there is no needing to worry about calling your credit card company, and waiting for another card to be mailed.
apon departure, you can tell the cm's at the front desk that you would like all charges for card X to be charged to one credit card, and then card Y to be charged to another. but make sure that you tell them that you do not want express check out. otherwise, all charges made to the room will be charged to that one card on file, and you will have to go in and change it anyway.
hope this helps...
good luck and have fun!
jen