I would stay onsite and no rental car. If you are truly in a hurry, you can always take a taxi from your resort instead of waiting for the bus. The few times we needed to do this did not add up to the cost of a car rental. At the deluxe hotels you can usually sleep up to 5 in a room, so 2 connecting or nearby rooms would really give you a lot of space. And the deluxe rooms (not sure if mods have this too?) all have hot water/coffee makers and mini fridges. So for breakfast we packed instant oatmeal packs and often had cereal and milk in the AM. Also, if you rent DVC points you will NOT have daily housekeeping (but if you rent villa through Disney you will get daily housekeeping). OTOH, you'll probably have a washer/dryer too. So consider ages and personalities of your daughter and nieces - whether washer dryer in your unit and kitchen are worth it. FWIW last time we were at BWV in a 1BR and I used the stove once to heat up leftover pizza and the microwave a few times to heat up lunch from dinner leftovers. Not sure if it would have been worth it had we paid full price - we had rented a studio and were upgraded, and the rate for the studio was less than for any deluxe hotel rooms, so we got a great deal.
This upcoming trip we are staying in a 2BR but we'll have my parents, sis and her partner, and 3 kids, a 5 yo and 2 infants. So we need the space and washer dryer.