The price would be the same, just who's name and who's paying for it. I'm sure you know all credits will be pooled. You could just leave it as is and pay for it yourself and make sure they don't use more credits than they pay for. You could also leave the 2 in the studio and move the 10 y/o there as well getting less credits and having less guests on the plan. Philosophically I have a lot less issue moving someone to the room to get the dining than I do moving someone out of the room to avoid the cost. I also suspect you'd save a lot more with the TIW than the DDP as long as you're not planning the CS plan.
i am uber scared about breaking rules at Disney for fear of retribution

I fear that if we step outside of the lines they'll strip us of our
DVC membership and possibly make us give up our first born!
When I had spoken to the CM months ago, they mentioned that each person can have the DDP charged to their credit card.
So I know that the numbers do not change in regard to whom is paying for the meal plan and how many people are staying in a room. And honestly, had the price not jumped from $15 for my niece to $53, everyone would probably just get it without any debate. But the reality is that my niece just isn't a big eater and to pay $350 for her for the week is a definite loss.
So I know if you remove the names from the process, we end up with 2 people not having a DDP.
But at least if I have the rooms set up according to the DDP, then everyone will be able to present their card legitimately at restaurants and snack spots.
In regard to TIW, that would be the best bet economically. The downside is that I would pay for every meal and then have to track down what the other 6 family members owe me. That's just not worth the headache. Once one of my girls hits the adult rate for the DDP, we'll def go that way...maybe even sooner.
The kick in the shins is that the folks that aren't getting the DDP are still going to have to pay for the pricey meals OOP...and ~$3\snack!
We do a solid 5 character meals, so you can see where the price adds up. Seems like the cost savings for the non-DDP family members will be negligible!
Good think I love my wife's family, huh?
So then looking at letter of the law versus spirit of the law, Disney really could care less about putting a name to a face as long as no one is cheating by sharing food and such.
