First thing I'd do is review/bookmark/make notes after reading the FP+ thread (Stickie?) by mesaboy. Be ready to book your FP+ the 60th day before you arrive (if onsite; if offsite 30 days). You have to have park tickets linked to your
MDE account to choose FP (sounds like you have a package, so all set there). Do you have MDE set up? All travelers listed in your MDE? If so do a test run: choose FP for next week, all 5 of you (then delete). You can learn if any odd IT issues with a ticket (I've had it happen).
You really want to book FP+ as soon as permitted for the entire trip because you are assured 3 rides without a long wait. (You'll notice when reading the FP stickie that you can only choose 1 'tier 1' ride in Epcot, HS and now AK. So if DDs like Frozen, at Epcot you'll see via mesaboy stickie that getting FEA (Frozen Ever After - its a newer ride) FP will save you far more time than Soarin or Test Track (do those at 'rope drop' - you save the most time in line if you can get to the park before it opens). Trust me, if you have Frozen fans you'll regret choosing anything other than FEA for your tier 1 FP at Epcot.
I felt so bad for a single mom and her sweet son who were on their 1st trip to WDW, and chose Living with the Land as their tier 1 at Epcot (it rarely has much of a wait). This was before FEA was open, and Test Track was down, so Soarin waits were over an hour. Don't let that happen to you - see the ranking in that stickie about which will save you the most time.
Do the xmas party midweek - usually quieter than weekends (but you never know). MK will be quiet that day, so if you have a ticket for every day of your trip its nice to spend the morning there, take a pool/hotel break, then back for the party. The party ticket lets you in at 4pm (unofficially; but its been true for years), so if you don't have a park ticket for that day then just do a nice out of park breakfast, pool, and book FP for 4pm at MK and go to the party (you can book FP until IIRC 7pm on party nights).
HTH! Oh and be sure to customize your MagicBands - you don't want any sad gray bands, and its so fun to customize with the kids online, and then open the box when they arrive.
PS Many people choose ADRs asap (you can do that 180 days ahead for entire onsite trip), then make FP+ to fit that, but I find it too exhausting to deal with all those logistics so we just wing the dining. That definitely won't work if you want Cinderella's Royal Table at 8am though!