I've moved house lots of times, but never with children. However, I would think that having the children out of the way would be best. Can you arrange for them to be at a friends house all day? A sleepover at a friends would be even better so that you don't have to worry about getting their rooms or the bathroom sorted for that night.
Not used a packing service before - I presume they unpack for you? If not, it might be an idea to mark out priority boxes that HAVE to be unpacked on arrival e.g. favourite toys, stuff for nappy changing, spare bedding, essential clothes.
You could pack up a suitcase for each child with above essential items perhaps? Then at least you'll know where the basics are.
If the children aren't at a friends, invite your entire family to somewhere for dinner, or head out for a pizza or similar. If the children aren't around, you could have a take-away, but from experience, it's really nice to escape from the chaos for just an hour, so taking youself + spouse/partner somewhere else for dinner is a good idea.
Nominate one room (or an area in more than one room if you don't have a spare room) for piling stuff that you don't have time to deal with straight away e.g. books and pictures, ornaments and so on.
Maybe to get the children involved, you could ask them what one thing is important to them to have sorted out quickly in the new house, e.g. by Christmas day, or by the time the guests arrive. It might be something really simple that would help them feel settled.
As far as lists are concerned, I would make two lists - one 'priority' list and one 'can wait' list so that you have clear in your mind what you need to focus on. Otherwise it's easy to get lost in the chaos.
Plan activities out of the house for the few days before Christmas for the children too, so that they are occupied and you have time to focus on the house.
Hard to add much else without knowing what the packing service entails, but hope this helps, and good luck!