You already bought tickets so FD is not option anymore. You got a great deal on lodgings so now just think of all the other stuff. Check out allears.net for menus, see what your family would like (and the prices) and pick one or two must do places. At MK The Plaza is a the cheapest TS and it is pretty nice. At Epcot you could go to Via Napoli and get a couple of big pizzas (more expensive than delivery but not too bad compared to other TS restaurants at WDW). Epcot also has the best CS places in all WDW, on those days I would not pack a lunch
Be our Guest is the hardest restaurant to book right now and will most likely be booked by the time you get to book it (another perk of staying on site is the 180+ 10 day window as opposed to just 180). But BoG is also open for lunch, it is still a counter service (unless something changes after Feb 25) but one of the nicer ones and if you would like to eat inside the castle this is a good option for saving money.
If you want to do a character meal go for a late breakfast - they are the cheaper meal and by choosing a late time it could easily count as bfast and lunch. If you do not want to cook every day you could always order pizza etc and have it delivered.
What I do when we go to
Disneyland is check the restaurants nearby and buy discounted gift cards for them (check Giftcardgranny for best rates).
You still have time to join a rewards program like Swagbucks or Perk which reward you for taking surveys, completing offers, watching videos etc. Their rewards vary but they both have restaurant cards you could use off property and even some restaurants on property - Rainforest Café, TRex, and Yak & Yeti (at AK) cards can be found on both. Swagbucks also has Paypal rewards. I get Paypal and buy Disney cards through Target.
Check Priceline for cheap van rental from the airport. Deals can be found, we got a car for $7 a day. I know vans are more expensive (had to rent one a couple of times) but keep checking, Sept is slow season.