We've been that week before, and parks don't get really crazy until about the 23rd, so do a MK day before then and try to hit the headliners. Also, definitely do rope drop every day you can haul yourselves out of bed. Avoid MK on Christmas Day - the one time we tried it we got there at rope drop, waited 40 minutes in the line at what was then Main Street Bake Shop, and when a cast member said we should expect that would be our shortest wait all day, we went to Studios and had a ball (crowded, but not ridiculously so).
At EPCOT, you could pretty much spend a whole day just listening to the storytellers, and because they're outdoors it's a good choice for afternoon when lines at other things are crazy. Norway is absolutely not to be missed; we also especially like Italy, Canada, and France.
Mini golf is also a good afternoon option - take the bus to Blizzard Beach and it's about a 3 minute walk to Winter Summerland, which has a Christmas theme. Fantasia Gardens is fairly close to EPCOT but will probably be quite crowded.