Yes, you can share at TS restaurants where you order from a menu. The only exception to this is Via Napoli which will not let you use 1 credit to feed 2 people. Also, if you are interested in the pizza, you can only order the individual size pizza when using credits and you cannot combine credits to order the larger sizes.
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, luau, Mickey's Barbecue, the family platter at Whispering Canyon Cafe, Fantasmic! Dinner Package and the Candlelight Dinner Package.
Sharing credits is a great way to extend the dining plan or to dine at the 2 credit places. Signatures are 2 credits per person so if you share at a sig you will be charged 2 credits for one entree/dessert/non-alc beverage.