This house does accommodate 12 people, I just dont recommend it. We had a 11 and with only 2 bathrooms its really hard. One shower has very low water pressure - girls with long hair dont use (you will never get the shampoo out). We did blow a fuse in the house and we couldnt get to the breaker box because it was in a locked closet.
With all that being said, the house was in very nice shape and we loved the back yard. With no air conditioning we had to have the doors open and we thoroughly enjoyed the backyard.