Hi, Natalie!
December is a very popular month for trips to Walt Disney World because that most magical place simply bursts at the seams with even more magic during that month. As such, specials tend to run prior to holiday weeks at WDW. However, that is subject to change; thankfully, though, Guests who book directly through Disney can cancel their original reservation for a full refund if cancelled at least 6 days prior to arrival, allowing them to book a special and get a full refund for an earlier reservation. No worries there!
Because you are a family of 6, I suggest that you look at this post,
Rooms for 5 Guests or More, to see the options you have for accommodations at WDW. There are so many from which to choose, with at least one for every vacation price range, so check out your options! You'll love the flexibility and convenience of staying at a WDW resort.
For accommodations adjacent to the monorail, consider one of my Disney Vacation Club Home Resorts,
Bay Lake Tower at Disney's Contemporary Resort. A family favorite, this resort will put you right next door to the magic of Magic Kingdom while offering your family all of the conveniences of home. A 2-bedroom villa would enable you to place four family members in the 2nd bedroom, with 2 in the master, keeping the living area open. If you need to separate those four, the living area has one queen-size sleeper sofa plus one sleeper chair, too. The beauty of this space is that it comes with three full baths, a full kitchen and a full-sized washer and dryer, as well. We throw in two loads of laundry each night and never check a bag, Natalie; going home with clean clothes is a beautiful thing, too.
Send me another question if you'd like more information on other options, too, Natalie. I'd love to help!