In my parents house, anyone who sleeps under their roof and "still believes" is welcome to put out a pair of socks/tights on Christmas Eve (we never had proper stockings!) and see what they get next morning. Always still half a fruitbowl (a red apple, green apple, perfect banana, kiwi, mandarin and an orange), a 1lb box of a favourite sweets, and a book. The youngest "child" turned 30 recently!! I don't think any of my siblings who has stayed "at home" has yet refused to put out a stocking. (I haven't slept there on Christmas Eve since the year after I got married, so 14 years ago). I am actually considering doing a stocking for DH this year that DD will help with, as a surprise but not from Santa (and she might tell him as secrets are SOOOO not her forte, so I might get one in return
).
We do the Christmas Eve hamper in our house - only 1 DD, but DH and I also get new PJs and slipper socks in it. And while DD gets a suitable child's hot choc mix (I usually try to get the "ice block of choc on a wooden spoon" type), DH gets a chilli one and I get the one with a little syringe of amaretto stuck into it!! Yum!!
While you DCs may be too old for it now, DD is only turning 9 so still wants us to read "Twas the night before Christmas" at bedtime.
There are so many fab board games out now. We play Q-bitz, jenga, monopoly, cluedo and I know I saw some great and very different ones in a shop locally here, Cogs which were good for all ages.
A great big jigsaw to work on together underneath a board? So the table can still be used for dinners, but the board lifted off and jigsaw continued in quiet times?
Is there any particular programme or film that the DCs love, or would agree to watch together? Make it a special time, with nice drinks (glass of wine, non-alcoholic cocktails, proper lemonade) and some popcorn or choc or favourite crisps etc? It doesn't have to be seasonal, just making it family time.
Get the DCs to help out with some prep work together at some point. Maybe they might be interested, if asked, to do some baking together on the Eve, like a yule log - or maybe even they might like the responsibility of doing a particular dish (traditional or a new one to the house) for Christmas Dinner, or doing the catering entirely for another meal for everyone?
Ask them too, what they like and don't like about Christmas. What they might be interested in doing differently. What they want to keep.