Any of these itineraries is certainly doable, esp. w/the development of companies like Easy Jet, Ryan Air, etc... a couple of things to consider:

Rome during Christmas - a variety of the sites you'll want to visit (i.e, the Vatican Museum) will be closed not only Christmas day, but a # of other religious holidays as well as regular closing days (usually Mon or Tues) therefore if you choose Rome you'll want to plan the rome days carefully

Two weeks is more than enough time for Paris/Rome, but to really "see" Prague you'll need more than 2 nights