I think those are seperate issues. You must be able to pay for some out of pocket, as the dining plan does not cover all your meals. It would be impossible for a restaurant to "force" you to use a TS voucher for everyone in your party at a meal, as perhaps some will use the TS vouchers at a later meal (or earlier meal) that day. The plan itself tells you that anyone in your party can use any of the credits at any time, as long as there are credits left. In fact, the CMs at the resorts were told by their managers to assist the guests at check in by explaining that they could pay out of pocket for their children, saving their TS vouchers for more expensive adult meals. Unless they actually change the plan language itself, of which I have seen no evidence, then they cannot disallow you to pay for some of your party out of your pocket.
I concur that sharing meals is not on the plan, so that is an issue up to the indvidual CMs at the restuarant.
Regarding the issue of using credits for those not on the plan, I was just reiterating what was told to me by a manager at Coronado back in March. I had a question regarding a situation at one of the snack carts in the MK. It wouldn't allow me to buy 5 water bottles. The manager stated that the number of bottles didn't match our dining plan party, so it wouldn't allow us to buy them. He said that the system is built that way so people can't by others not on the plan, meals. A server at Whispering Canyon, on another board, confirmed this. I know that the CMs obviously have a way of getting around this (because of the reports of people using more TS credits than people in their room), but it clearly is against the rules and is built into the computer system this way. I found that language on the plan documents (which is very ambiguous, I agree), as the closest I can see to this in writing.
The one question I do have, however, is there any objective proof that the dining plan language will change to seperate child and adult credits? Some have suggested so, but I haven't seen anything in writing to this effect.