There aren't any very good answers. Everyone grieves in a different way. I'll tell you my story.
My mom died in 1993, just ten days before Christmas (and three days before my birthday, the 18th of December), and it was good to have celebrations to keep our minds off her death, her funeral, etc. We buried her with our Christmas presents to her. So you can imagine that we were still pretty shellshocked. Especially considering that my mom died three months after being diagnosed with cancer. It was all a blur for me.
The following year was harder--the whole year after her death, not just Christmas. I wore a necklace all year that my mother gave me a few months before she died. I graduated from high school (I decorated my cap with glitter that read "Hi Mom") and went off to college. The anniversary of her death was TOUGH. I cried and cried. At the end of that first year, I stopped wearing the necklace. I think somehow I was done with the intense mourning.
I think the death of someone you're close to isn't something you "get over", it's something you get used to. You learn to live with the grief, you remember the good times when the person was alive, etc. I don't dwell on my mom's illness, I think about how she taught me to wink and called me by a special nickname and so on. I know she'd hit me with a lightning bolt from above if I used her death as any kind of excuse for acting like a jerk or going nutso.
I like to concentrate on what she'd wish for me, for the whole family. She wouldn't want us to wallow in our grief. But I still grieve. And I still cry. The day my mother died will always be the worst day of my entire life. (I hope.) It would be totally okay for your whole family to break down bawling while opening Christmas presents. It'd be normal to cry in a mall while buying gift wrap. It's as unhealthy to keep things bottled up as it is to endlessly dwell in sadness.
Anyway, I want to wish you a Merry Christmas. I know your mom is there with you in spirit. I feel like my mom is always with me.