Are you able to share meals at all table service restaurants?

I believe you can. I know my sister and I have each gotten apps and then shared entrees at a few places.

To add to what Drince said....
Yes, with the exception of buffet's.

I am trying to figure out if the Disney Dining Experience card is a more practical purchase than the Dining Plan. Are you able to share on the Dining Plan?

Obviously, no sharing on buffets (but I rarely do them, so I always forget to mention them).

I've heard mixed-info about sharing on the dining plan. Personally, I don't see why they should care, as long as you're ordering the appropriate kind of meal for the dining plan.

And you can use both the DDE and DP together, the DP to pay for the 'whole meal' and the DDE for the out of pocket things (like the drink for the second person, and if you're getting appetizers or whatever)

I am trying to figure out if the Disney Dining Experience card is a more practical purchase than the Dining Plan. Are you able to share on the Dining Plan?

It all depends. You can share is you are doing pre-plated entrees, as opposed to a buffet or family-style meal. You need to figure out which is the better deal, depending on the places where you will actually be eating, and the types of meals you prefer. We did just the DDE card, the last couple of trips, and I think it worked out better for us. For example, at the California Grill, three of us shared a platter of sushi, two of us decided to get two starters, instead of an entree, three of us had a drink at the bar, and shared a bottle of wine, and all four of us had dessert. Our dining that evening did not fit neatly into the parameters of the Dining Plan, and we just got the straight discount, which included our alcoholic drinks. In March, instead of having lunch, we had afternoon tea at the Grand Floridian, some of us having a regular menu item, some ordering a la carte. This meal would not have been covered by the plan, but the straight discount applied. If you are planning a lot of buffets or other price fixe types of meals, the Dining Plan is probably a good option. If you prefer to share an entree, or like to make a meal out of appetizers, then the Dining Plan won't work well for you. My kids do not enjoy most of the pre-plated kids' meals, which are their only option on the dining plan, and, if we are not doing a buffet, we often just buy an adult meal, which they share.

For the first week there are 5 of us and I have booked 5 out of 7 days for table service. The second week we have not booked. We are switching hotels so we could do the dining plan the first week. Does the dining plan expire when your initial reservations does or could we carry them over the second week?

Dining plan expires at midnight of the day you check out of the hotel that it's associated with.

Thanks for everyone's help!! It is a little bit clearer now! Luckily we have a few months to make our final decision.