No, you can use cash everywhere at the resort - that's no problem! (trust me!

) .
If 3 families are in a BC, you -being the member - can decide who get's room keys that have charging abilities. The system will track charges by card but apparently hold you (and your credit card) responsible. I believe the credit limit is $1500 before the resort will automatically process a charged to your credit card - so, either before you reach $1500 in charges, or, at check out, you can get a print out from the front desk of your charges then make "payments" on your room account (ie family one's card charges = $200, family 1 can make a payment to the resort for the $200 and so on ).
Basically, VB works exactly like it does at WDW.
I hope I'm not confusing you!