John, unfortunately, nobody can answer that exactly.

My best advice would be you can ask, but don't plan your ADR's around it -- and be prepared to pay OOP for a meal or two if necessary.
Lots of families share meals, both on the
DDP and paying OOP. A few of us specifically wrote to Disney Guest Relations. I gave the scenario of 2 adults, both on the plan, sharing 1 TS credit (which we often do at other restaurants). Another person, bicker, asked if 4 adults could share 3 TS credits. The answer from Disney Guest Relations was clear: guests on the DDP may not share meals.
Many, many people on the boards will tell you they have shared meals on the DDP and had no problem, that the servers were very accommodating. The DDP brochure states that you can't use credits to purchase meals for people not on the plan, and you cannot use children's credits to purchase adult meals -- but it
does not say you cannot share meals amongst your own party. If Disney truly wants to prevent families sharing credits (thus banking credits for a 2 TS signature restaurant or dinner show), they may change the brochure in the future, but it could be a real headache for the restaurants to police and enforce it.
There are a couple of recent threads that discuss this in great detail:
http://www.disboards.com/showthread.php?t=1376421
http://www.disboards.com/showthread.php?t=1383495
http://www.disboards.com/showthread.php?t=1382695
HTH...