Here's the thing...

TIW is available to DVC members, and needs to be in the name of a member. The card is not usable by anyone other than the person who's name is on the card. So while you can get the card and use it for everyone in your group, you will have to be present whenever it is used (they will check ID). As long as you're all together, it's cool. Won't work if you're not. Alternately, since you are making both reservations with DVC, you can get the dining plan for both. You can call member services to do that.

You can definitely have both the dining plan and TIW, but just be aware of how you have to use them. You may well be better off with just using TIW.

Steve