Yes you will be able to share meals and use only 1 credit between the 2 of you at the TS where you order from the menu. There are a couple of places (Via Napoli is one) where you won't be allowed to do it.
Also, you cannot share at buffets, all you care to eat family style places, CRT, prepaid dinner shows, and the Fantasmic Dinner Package. At all of these you will each be charged.
Between the 2 of you will have 6 dining credits per day. Even using them at sig restaurants and other 2 credit meals, it sounds like you'll have a lot of credits left over. Considering the price difference, if you want a dining plan you might want to consider the regular
DDP. You would have to pay for the appetizer OOP, but that would still be less than the difference between the cost of the DxDDP and the DDP.
Most likely, however, with your eating style I think you'll probably save more by just paying OOP for your meals.
We've done both the DxDDP and the DDP. We prefer TS meals to CS and when on the DDP end up paying OOP for some TS meals so we decided to try the DxDDP. We did breakfast or an early lunch and a late dinner, mainly at signature restaurants, almost every day. Even with just 2 meals a day it was so much food and took up too much time. I doubt we'll ever do the DxDDP again.