One thing to consider is limiting the amount of time your loved one spends with people and also keeping the number of people they are with at one time to a minimum.
Consider giving them a place they can go to get away from all of the commotion and relax. It can be very overstimulating for someone with dementia when there is a lot of noise—even the happy noise of the holidays!
Consider how you can maintain this routine as much as possible. “Less is more” is probably the best solution for helping everyone in your family, including your loved one, have happier holidays.