In our family, whenever someone is confirmed, the whole family is invited. Our family is spread out into several states, so we usually all make a big weekend of it (Fri evening-Sat-Sun). We BBQ Friday or Saturday and spend time visiting, playing games, shopping, etc on Sat.
On Sunday we all meet at church (usually 10:30) and the family all sits together (Confirmand sits w/ Confirmation class). After church, we take pictures of the Confirmation class and the Confirmand w/ godparents, parents, banner, etc.
Following that we have a "party" and invite all the family before they head home. Usually it's a cold cut tray, veggies, meatballs, salad, chips, punch, and cake (shape of a Bible or shell). Sometimes we put out a photo collage of the Confirmand over the years - but you wouldn't have to.
Usually all the aunts and grandmas contribute to the food (Grandma makes meatballs, an aunt makes fruit salad...) so it's not an overwhelming event to prepare. We also may invite close family friends (pseudo-grandparents, Lutheran school teachers, pastor...) depending on how many family can make the trip. We also have been able to use our church fellowship hall for Sunday's lunch (which is convenient).
Sorry, that was a lot of info - but wanted to give you some ideas.