Yes, you need to have 10 rooms booked. They do not have to be exact same nights but at least one night must have all 10 rooms. The discount is around the AP discounts or better on the values for tthe dates I was quoted. You can also buy meal vouchers as a group but I didn't look into it because we couldn't make it to the 10 rooms. Also one person guarantees all ten rooms on one credit card.