Couple things - just realized that is a
MVMCP night(Christmas party - extra ticketed event) so Magic Kingdom will close at 6 pm unfortunately, except if you buy an extra ticket to the party. Do you would have to leave the park at that time - you could stay to watch the castle lighting, usually around 6:15, then head out. The good news is party days are often less crowded during the day, but you would want to be there at opening to get the most out of the day. Currently it is scheduled to open at 9, so you'd want to be there at 8, but good possibility from past experience that it may end up opening at 8(possibly 7) so just something to consider if driving in from Jacksonville (I am guessing it's a couple hours travel time?). Don't know if you have any flexibility to do Wed. for a full day. If you do stick with Thursday, after the park closed for you, you could hop the monorail and check out the Christmas decor at the Grand Floridian hotel - giant gingerbread house is really cool. You could also try and get a late dinner reservation at one of the resorts on the monorail - your nephews might enjoy Ohana or Chef Mickey's, or something more casual like the Wave at the Contemporary, depending on your interests and budget.
The key is to make plans now - buy your tickets, then you can go onto Disneyworld's website and make an account. You can then link your tickets to the My Disney Experience section(top right on page). You will list all your guests as Friends and Family, and link a ticket to each person. You can also then download the app on your phone. You can then go on at the 30 day mark at 7am to make Fastpasses(and of course anytime after that!). Some may be unavailable, since onsite guests can do this at 60 days, but you can grab the best ones open for your times and interests. You can then modify as it gets closer, since people change plans, especially in the days before, and even day of, to get something else you wanted. With 8 in your party it may be harder to get some, but you can also break your party into 2 groups of 4, and get times close to each other, and still ride together. The FP has an hour window to use it, so you could get 1 for 10am-11am, and the other for 10:15-11:15am, and could all go on once 10:15 hits. The ride you want to look for first is the Seven Dwarfs Mine Train, a small coaster, which will have long lines all day. If it is not available, you can plan to do that first thing if there at opening. Then Peter Pan is the next one that gets very long lines, but is not that exciting, but your nephews may not be into that. Are they thrill seekers? Enjoy coasters? The next three rides most people get FP for are Space Mountain(dark coaster), Big Thunder Mountain(basic coaster), and Splash Mountain(log flume with big drop at end). Any of these, plus Haunted Mansion, Buzz Lightyear, and Jingle Cruise(normally Jungle Cruise, but done up for holiday) are good ones to start with. Try to get ones between 10 and 1, when lines get longer, then when you've used your third one, you can try for a 4th, then 5th,etc while in the park. If you can, look at a park map first, try to get things close to each other(like Space Mt. and Buzz) if back-to-back, so you don't have to run from Space over to Splash, and then back to Buzz for example, to save time and energy. Sorry - lots of info. to digest I know! Feel free to ask questions and this FP FAQ thread on here may also help:
https://www.disboards.com/threads/fastpass-frequently-asked-questions.3491680/
If you want a dining reservation you can try for that now, as soon as you have an account set up - don't need to have tickets for that, but will need to guarantee with a credit card - you can cancel up until the night before with no penalty, so if you see something, grab it, and can then change as needed. Again, they may be hard to come by right now as people can make them at 180 days out, and you have a party of 8, but things pop up, again especially as it gets closer.
. Generally speaking, you will want to try to arrive an hour before opening and get your 3 Fastpasses set up ASAP for the rides that will have the longest lines (from what is currently available).
