At most TS restaurants where you order from a menu you can share meals (use 1 credit for 2 people or 2 credits to feed 3). One exception is Via Napoli which is very strict when using the dining plan. At Via Napoli you cannot use 1 credit to feed 2 people. Each person would have to use a credit. Also, if you are ordering pizza, you can only order the individual size using credits and you cannot combine credits to order the larger sized pizzas.
You cannot share and everyone 3 years and older will be charged credits at buffets, all you care to eat family style restaurants, CRT, Akershus, the dinner shows (Hoop De Doo, Spirit of Aloha Luau, Mickey's Backyard Barbecue), the family style platter at Whispering Canyon Cafe, the Fantasmic! Dining Package and the Candlelight Processional Dining Package.