That sounds so nice, what a great sis you have. You have lots of choices. Unless, as I mentioned before, you're going to be there on a crowded holiday, you should have no problem parking at either the Boardwalk, Beach Club or Yacht Club. All 3 are within a few minutes walk of the Int'l Gateway, which brings you into Epcot between France and the United Kingdom. A popular choice is eating at the Rose & Crown pub. You could get lucky enough to have a patio seat with incredible view of the fireworks. You are right on top of them. There's also a bar that has limited food service inside the restaurant and you can pop out and view Illuminations. Or if you're early enough, you can snag a patio table in the UK Beer Garden, grab some takeout fish & chips and a tall frosty cold one. The Beer Garden does get very crowded though, so probably not a good choice if you're looking for something quiet.
Have you checked out what's available at the Boardwalk area? There's a couple of clubs, restaurants, galleries, snack places. It's a wonderful spot to spend a few hours after Illuminations. We do this on nearly every trip. You're not just limited to what's at the Beach Club, although I love Beaches & Cream, so that's always a good choice.
So much to do and so little time....