Call MS. They may be able to help you. You could pay for a few nights with points and the rest of the nights with cash (if there is availability). You cannot use points and cash for the same night, though. If MS can book for you, the reservations will be linked such that they appear as one continuous reservation to the resort. It will look and work just like a reservation made entirely with points. IIRC, not all 3 bedroom villas are available for cash. SSR is probably your best bet, but there may be others available as well.
If you have to book the cash nights via DRC, it will be more complicated to match them with your points reservation. You would have to make sure the cash reservation is for the exact same booking category as the points reservation. For example, if the points reservation is for an AKV-Kidani standard view Grand Villa, the cash reservation would have to be for the same exact thing. (If you book through MS, the CMs there will make sure that happens). Each reserving entity (DVC & DRC) would have to put a note on the reservation that it made that cross references the other reservation number. The note should also say that it's a continuing stay and include a request to stay in the same villa. You still might have to go down to the front desk to check out and back in again between the cash and points reservations.
Good luck. Sounds like fun.