If you stay at BCV, you will need a 2BR for 8 people (assuming 6 children and two adults.) You'll have a master bedroom with a king size bed, a second bedroom with a double/queen bed and a double/queen sleeper sofa, and a double/queen sleeper sofa in the living room as well. (I'm not sure if these last three are double or queen size, but someone will know in a minute!!!!) In order to rent this unit, you would probably pay the going rate of $10.00 per point, and the per night cost would be 50 points for Sunday through Thursday nights and 106 points for Friday and Saturday nights. So a weeknight would be $500.00 and a weekend night would be $1060.00. A week's stay would be 500 x 5 + 1060 x 2 = 2500 + 2120= $4620.00. You can check the WDW website to see current rack rates for this room, but I believe this would be a substantial savings over paying rack rates. I don't know what the Contemporary would be, but you can also check it on the WDW website.
The Beach Club area is so wonderful - great pool, fantastic access to Epcot and MGM, excellent restaurants and just a fun atmosphere. The Contemporary does, of course, have great momorail access tot he MK, and a castle view is wonderful as well. In your situation, I'd vote for the BCV 2BR, but either way you'll have a wonderful trip!!!