Skye is amazing but most of it closes down for winter because of the weather. How about near the Cairngorms? Beautiful walks and scenery and most is accessible due to people who come in for the skiing.
We did 9 days in a campervan this summer round Scotland and it wasn't enough!
We did Edinburgh, Aviemore for the Cairngorms, Cromarty for the Moray Firth dolphins, Loch Ness, over to Fort William /Mallaig for the Harry Potter train, Camusdarach on the West Coast, Glencoe, Loch Lomond and down to the Solway Coast. We loved it all (we had amazing weather though!). I don't know what would be best at Christmas but I'm jealous!
They have a reindeer herd on the Cairngorms that you can visit.
Aviemore sounds good. Thinking that it might be a bit of a waste though if we aren't into skiing (although kids might fancy other snow activities). Any surrounding areas near to Aviemore that might be good? suspect they might be a bit more affordable too.