Love NYE around WDW. My advice, don't let the Internet scare you. Yes it is crowded, but generally speaking park hours are long, the weather is good, and Disney is actually pretty good at handling the massive crowds. Do things get stretched to the max? You bet. But maneuver around whatever you're doing with an open mind, knowing you'll maybe need to zag instead of zig, call an audible, or whatever you may need to do in that moment, and it can great fun.
You may already know this stuff, but MK does their special fireworks 12/30 and 12/31 at 6:30pm and 11:50pm. The 6:30pm shows use the traditional behind the MK launch points, the 11:50pm shows are the "expanded" shows where they launch from additional points in the Seven Seas Lagoon. The angle/view from WL isn't my favorite for fireworks among the MK resorts, but it's not terrible, if you decide to catch any of the shows from there.
A word of caution that sometimes catches people off guard on these special days, for the late show boat service is suspended 45 minutes before and 30 minutes after the late show due to the additional fireworks launch points. Waiting for them to get the clear to start up the boats again after the show (when by that point you just want to be home/in bed) can be a little tough, so opt for the bus if ever in that situation. Or just find something else to do to let things clear out.
All the resorts have a slate of activities for the evening. Usually crafts, games, entertainment, a DJ, often some character appearances. They do tend to slant for the younger crowd, but can still be fun for all ages. Disney doesn't publish any of this, so you have to look around online for people that posted pics of the activities schedule they put up around the resorts that day.
Personally, with your ages I'd be more into heading to Epcot on 12/31 despite your experience many years ago. In recent years as mine have been getting older and more able to hang in that sort of vibe we've been leaning more towards being in the parks than being at the resort, but sometimes we end up making that call on the fly depending on the mood, weather, etc. It can be nice and warm and it can be freezing.
I do agree with a PP to try to make some dinner plans on 12/31 in advance. You'll be happy you have something scheduled. Dining on the fly is possible, but can be more limited.
Sorry a little long. Whatever you do, I'm sure it will be a great family time.