It's perfectly fine to share a meal, if you like. We've done it many times, and have never had a problem.
Keep in mind though, that this isn't a possibility at any of the buffet or family style restaurants, since at these places you are paying for a seat at the table in a setting where the food is shared by all. You also will need to pay per person at any restaurant that has a set/pre-plated menu (Princess Storybook, and Cinderella's Royal Table).
If you are unclear about which restaurants are buffet, family style, or use menus, you will find this information in the description of any of the restaurants on the
WDW web site, or you can search for the page "Buffet and 'All you Care to Eat' Dining at WDW" at www.allears.net which includes a very handy list of all the buffets, etc (in your case, this would also be a list of restaurants where you won't be able to share meals).
Hope that helps. ºoº