Howdy Jennifer! Let me begin by thanking you for all of the great questions you have submitted to the panel!! You are appreciated more than you know and I hope several Guests have been able to enhance their vacations by the questions you have asked.
Regarding
Mickey's Very Merry Christmas Party: you will be able to pick up your tickets anytime after arriving. In fact, I would recommend it. If you are at Magic Kingdom and see that the lines by Guest Relations are relatively short, you might take a few minutes and get your tickets then so you can maximize your time the day of the party.
I needed some guidance and asked my fabulous fellow panelists for some insight regarding your other question. Without hesitation, Chris G, Diane L, Doug I and Mona Leigh G all suggested
Hoop-Dee-Doo Musical Revue, though it was also stated that you (and, particularly your younger two kiddos) will also enjoy
Mickey's Backyard BBQ.
Hoop-Dee-Doo Musical Review is described as a "hilarious, high-spirited hootenanny the whole family will enjoy, accompanied by a finger-lickin’ countrified feast." The panelists I mentioned loved Hoop-Dee-Doo and agreed it would be a great experience for everyone in your family. I know you and your family will enjoy every fun-filled minute!!
Thanks again for your question and please let me know if you need further information. Have a magical day!!