We often have Christmas as just us 3 (DD14, DH and I), and had it a few times as just 2 before she arrived. We do have larger extended family gatherings some years - but it's either all or nothing (we live 2.5 hours from family, they are 15 minutes apart - so it's a nice relaxed day for 3, or a manic day involving 2 full turkey dinners!!!).
For our "at home" years:
Well every year we have things in the run up that should still be possible this year - walks in the woods, crafting, baking, movie picnic on the carpet, driving round to see the houses lit up (there are a few that go all out locally) etc.
Christmas Eve, DH and I may have to go into work (so DD will come with me if so, and we buy her birthday cake in M&S en route home).
But in the afternoon, we are home and we do the prep work for turkey dinner together. (We like roast turkey - but have done other things some years to try, but always do the prep in advance). So its a communal peeling of potatoes/veg, making stuffing (with DH ringing DMIL for the recipe as he's forgotten it again - another tradition!), and DD baking cookies for "Santa". We usually have the radio going at that stage, with Santa on his phone in and preparing to take off, although it was Spotify music last year.
Baking on Christmas Eve may sound mad. But I do a batch of those cookies earlier in December and freeze half the dough (it's a "slice and bake" type dough, not "roll out and cut"). So if we have time and energy, DD can get out the ingredients and make them from scratch. But if we've been doing other things so short on time or are too tired, I get out the frozen dough and we just slice and bake that. DD has been making cookies to that recipe since the year she was about to turn 1 - when she mixed the eggs before adding them, and got flour all over the kitchen while I did the work; to slowly getting more involved to the point that I am totally superfluous! 
And even though we all know who "Santa" is, DD has never formally admitted it and still puts out her stocking every year (for the small things - larger gift is now from us blatantly). So she wants to make sure the cookies are still done for Santa's helpers.
Dinner on Christmas Eve is "platter". Basically lots of cold things, and sometimes a few hot like sausage rolls etc, on the table for everyone to help themselves. A more luxurious buffet than we would normally have (and not everything every year - just enough to satisfy us nicely) - a mix of sliced and cured meats (parma ham, braseola, salami, proper corned beef or spiced beef etc) and fish (smoked salmon, prawns, squid rings etc), sometimes pate, dips like salsa and hummus, breadsticks, sticks of carrot and peppers, cherry tomatoes, olives, sometimes a green salad, crusty bread, nice crackers, the Christmas cheeses are opened too....
After dinner, we maintain the Irish tradition of the youngest lighting a candle to show weary travellers that there is room in our Inn (but ours is not in the window, we have it on the mantlepiece). We take a few quiet minutes as a family to reflect on the year just finishing, the good and bad points of it, and remember those no longer with us, before having a short family prayer (we're not terribly religious but it's nice to do at that point in the year).
Then DD gets out the Christmas Eve hamper, which has new PJs for all of us, a Lush bath bomb each for DD and I (and sometimes a nice shower gel for DH), posh hot choc (lump of chocolate on a wooden spoon) for everyone, Christmas beer for DH and things that come out every year - DD's stocking, her plastic Santa plate and glass from toddlerhood (for Santa's snack), her snowman covered hot water bottle (used all winter long), and the family copy of Twas the Night before Christmas from DD's 1st Christmas.
It used to be stocking and snack out, bath, new pjs for hot choc and a snuggle on sofa, then book read aloud to her in bed after that. Nowadays, the snuggle on the sofa lasts a lot longer and involves a movie, and last year we had no bedtime story reading for the first time (she did bring it up to read to herself though).
Christmas morning, we have the excitement of the stocking and a nice breakfast - freshly squeezed OJ, lots of coffee, we bake pastries (either Jus Rol ones from the tin or M&S ones from the freezer).
We have a leisurely time getting organised, showered, dressed nicely, before heading out to mass and to visit an elderly DAunt locally.
When we get home in the early afternoon, there is about 30 minutes of work as we turn on music, light the fire, turn on the oven, get the final bits of turkey prepped, throw a pack of M&S party food into the oven, open a bottle of wine and nice drink for DD, open crisps into a bowl, take out M&S food and put turkey in - and then relax. Presents get opened, there are occasional forays to the kitchen to baste the turkey or add the potatoes etc, drinks get topped up. We each need to ring "home" at some point so late afternoon seems a good time usually.
We eat about 5-6ish - whenever the turkey is done and rested. Making the dinner is a joint effort. The M&S nibbles earlier are our starter normally, proper turkey and trimmings main, and maybe later in the evening we will have pudding and/or cheese. Or maybe not, depending on how full we are.
Later, we sometimes play cards, or just watch tv. But as our lives are normally extremely hectic (and December can be particularly busy), 25th is the one day that we can properly slow down. As we often have to work on 24th and DD's birthday is 26th so we host neighbours and any family that travel. And there are other commitments and travel to be done the other days of the holidays, (we need to go down home to see both families for a few days etc) so that single oasis of calm is sooooo nice. We don't need to fill it anymore than that.