We have taken our family of 4 on two Christmas/NYE cruises so far (the last one on Solstice in 2019). Our two adult kids will not be able to make our third this coming December (Solstice again).
Here is a thread similar to yours from earlier this year (link). In it I posted my comments along with photos and links to the Celebrity Today that was issued for the two holidays which you may be interested in.
I think you and your family will enjoy your holiday cruise plus Silhouette is a nice ship.
Tipping the crew extra is a great holiday idea.
While Christmas is a bit understated in terms of how it is celebrated onboard, NYE is one big party spread across several different venues. Since your ship will be in the warm Caribbean on NYE, the pool deck will be where the action is.
If you look at the thread that I posted, you can see we have decorated our cabin for Christmas. To me, I think the only "don't" is not hang any lights out on the balcony.
You are going to definitely want to have your family's photo taken by the ship's photographer on Christmas Eve/Day by the Christmas tree in the Main Foyer.
If you have any questions, let me know.