What's the weather like? Is it very crowded (like in the summer? Any recommended places to sleep for 3 (our 16 year old son will be with us? Any advice would be great...
Weather is always a toss up. Could be nice, and maybe cold. Any of the weather web site will provide a forecast. I suspect with a new Pope, and the usual Christmas holiday crowds in Rome it will be very crowed. More so than summer. We like Hotel Sonya and Aberdeen when we are in Rome.
Yes, it's crowded, but much less annoying than when it is 37C-40C degrees! Avoid St. Peter's on Christmas Eve if you dislike crowds. We prefer to go to English services at Santa Susanna then to a nice Roman fish dinner, traditional on Christmas Eve.
For this Christmas? Make a reservation now! Choices will be limited as it is late. I like Booking.com as the availability is easy to assess and you won't be left chasing rooms that are not really available. I also like to recommend Cross-Pollinate.com for alternative lodging.