To book through
DVC/MS, at least one person per cabin must be booked with points. The others in the same cabin can be booked for cash. (The first two people in the cabin must pay the adult price - points or cash, even if one of the two is a child).
The cash price is the one DVC negotiated with
DCL and it may be more or less than the price a TA or DCL is currently charging.
IIRC, you must pay for the entire cruise up front - points and cash.
Best wishes -