We love the deluxe plan, but it is a lot of time and planning compared to the basic plan. Personally I don't think it is the best option if quantity is the only issue because three sit down meals per day take up so much time. I think the plan really works best for people who want to enjoy signature dining, rather than those who are thinking about 3 full meals every day.
I'd second Cathy's recommendation to up-age your youngest so that he can order adult meals. You have to pay the difference between a child's and adult's ticket, but that's only $40 or so and it is well worth it for a growing boy who isn't likely to be happy with the smallish kids' meals.
Beyond that, I'd place an order with WeGoShop or Garden Grocer to have some snack type foods on hand in the room without paying Disney prices for them. Nothing big, but just pop tarts or nutrigrain bars for the mornings, chips/prezels for evening munchies, and drinks. Remember you do have a fridge in the room so even things like string cheese work well, and if your boys are anything like my 12yo and his friends they'll love having it on hand. That frees your DDP credits to buy a quick service lunch, a full dinner, and a solid snack during the day.
You don't mention if you have dining plans in mind for your table service credits, but if you don't have that decided yet you might want to look for places that have fixed-price three course meals that are available on the DDP, as well as buffet and family style places that are all-you-can-eat.
I would also plan on a certain amount of OOP spending. Book a meal at Planet Hollywood to use the certificate that comes with your package, put some money on a Disney gift card for extra snacks and quick meals so that you aren't worrying over menu prices, and plan for the DDP covering most but not all of your dining expenses.