4 of us (me, wife, 2 daughters 13&11) are going to Europe this Christmas. Kids school choir is doing several concerts in Rome, Florence, and Assisi. We have to be in Montecatini on Dec 28th and we finish in Rome on Jan 3. The kids are out of school on Dec 19 and start back on Jan 6. We would like to fly over the day after kids (Dec 20th) get out of school and we can push the return flight back to Jan 4th or 5th if it saves a lot of money. We are flexible on the flight days. We live in Houston so need to fly out of here. We would like to spend first couple days in London. We probably would like to spend another few days somewhere in mainland Europe that would be closer to Montecatini. One other family is going early to Vienna. We could do that or some other city in Europe that would be good to visit during Christmas? I really am trying to save on the flights, so any suggestions on days to travel, ways to maximize points, tricks to get upgraded to at least economy plus would really be appreciated.

United has a direct Houston to Munich flight. There will be Christmas markets in Munich or you can easily train to Vienna or Salzburg from Munich.