We usually have some kind of jello mold using sugar free jello. Remember to use fruit packed in pineapple juice instead of syrup. If the recipe includes either cream cheese or sour cream, use the "lite" stuff (neufchatel) and plain yogurt - as they're probably watching their fat intake as well as carbs. Most people tend to plan their regimen to include some of the typical extras - so it shouldn't be too bad.
Instead of candied sweet potatoes - or in addition to - you might have baked sweet potatoes (we serve them with cinnamon & sugar/Equal), or something like FuFu. For the FuFu, cut out the sugar in the recipe, cut it in half, or simply substitute Equal since you won't be cooking it at that point.
We usually have at least one plain vegetable in addition to the green bean casserole, such as cooked carrots. Carrots are kind of sweet on their own. My mother nukes the carrots & puts a little ginger in the water to give them a little extra flavor.
If you serve garden salad, make sure you have a low-sugar type dressing (or plain wine vinegar & oil) available. Watch the "Lite" dressings, though - the way they get them low in fat is to increase the sugar!
I guess it depends on the people you are having. Some will eat "regular" food & da** the consequences. (You might as well not bother commenting if this is the case - they know what they're doing.) Some might "taste" the regulars, but appreciate something specifically for them. Some might not want attention draw to their "difference" - in which case offering 2 kinds of sweet potatoes or 2 veggies, etc. with a simple, brief explanation of the dishes might be a good idea.
Dessert is the hardest. You can get good sugar free vanilla ice cream. Sugar free apple or cherry pies are available at many bakeries. (Skip s/f pumpkin, though - they're usually awful.)
