With a price change and seat assignments being limited or unavailable on the airline website, this generally means that the flight is nearly full. This does NOT mean that you do not have a confirmed ticket on your flight. I do see that you have a confirmed ticket with your airline and a confirmation code.
Since you are traveling over the holidays, I personally would check the airline website within 72 hours of your flight as most airlines release some seats within a few days of travel. If you are still unable to select seats, show up to the airport a bit early and you should be able to get seats assigned prior to heading to your gate.
Thank you for leaving feedback and for being an Expedia Customer!
Sincerely,
Martin Gurth
Sr. Manager, Customer Experience
Expedia.com