Another option, if you are willing to go value, would be to get a family suite and another room at either Art of Animation or All Stars Music. Having one family in a suite would give you all a "living room" space to hang out in during the day. Then there's also offsite. You could definitely rent a 3 bedroom condo far cheaper than staying onsite. The last time we did this, it was $85 a night for a 3 bedroom, 2 bath condo with washer/dryer, full kitchen, living room, dining room, and a screened-in balcony. It slept 6 in the bedrooms and three more in the living room (Q sized sofa bed and a single couch). Yes, we rented a car and paid for parking at Disney every day, but doing this meant we could afford to go to Disney World. If we'd decided we had to stay onsite, we wouldn't have been able to go.
Also… remember that
free dining only gives you two meals a day. DD and I choose to share breakfast and lunch, and each use one TS meal a day, so we don't have to pay OOP for breakfasts. Some people get breakfast foods and eat in their room, others choose to pay OOP and get kids meals for everyone for breakfast to keep costs down. As kids aged 10 and up are considered "adults" for the meal plan, that might give you some extra food to share at different meals, if you want to stretch those food credits. There is no way that any 10 year old I know can eat a half chicken with mashed potatoes and veggie in one sitting, but that's what you get for one QS credit at Cosmic Ray's in the Magic Kingdom (and there's a similar meal at Flame Tree BBQ at Animal Kingdom).
Disney lets you bring food into the park. We always take our own water (or an empty bottle and get a cup of ice water from any QS location) and park snacks. This helps us limit ourselves to the one snack credit available through the dining plan- we all love Mickey bars, dole whips, etc., and don't want to skip them- because the cost of snacking can add up quickly. We bring in a variety of snacks, but try to avoid anything with chocolate or candy-chips because they melt and make a mess! If your kids won't drink plain water, get some flavor drops or the little packets of drink flavoring (think koolaid in a tube)- they have them at Dollar Tree all the time.
Look at the Disney restaurant menus either here or at all ears.net- or even on the Disney Dining website to decide if "free" dining is the best way to go for your family. It's only "free" because you have to pay rack rate for the room. THAT can get expensive quickly, especially as you need more than one room. Look at the menus and the prices, and decide how much it'll cost to do "free" dining vs. a discounted hotel room and paying for food. Our experiences with food at Disney is that they give you HUGE portions. I am a big girl and a hefty eater, and the food is more than adequate; as I mentioned above, DD20 and I usually share b'fasts and lunches if we are eating at Disney. Also, the dining plan includes desserts, and we don't eat desserts. That right there cuts down on the value of the meal plan for us.
Mousesavers.com has good tips and deals, and if you sign up for their newsletter you can get a discount on buying park tickets from Undercover Tourist (an authorized Disney ticket broker). They are the masters of walking you through getting a huge discount on car rental, too!
I am not trying to talk you into offsite vs. onsite, and if you are flying down you would probably need two vehicles if you are offsite with 9 people, which definitely will effect affordability. I am just sharing some things that we have found we can "tweak" to make Disney a more affordable vacation (and don't' get park hoppers, just saying this is a great way to save $540!).