That sounds hard.
Can you make changes this year as you are in a different place?
So, do you want Christmas dinner at lunchtime, or as the DCs are getting older, would it be nice as an evening meal?
In the afternoon (regardless of dinner timing), why not agree that you (DH, DCs and you I mean) are all going out for a walk to X place - and just go, lock the door, and PILs will have to go back to their accommodation. (You are going for an ENERGETIC walk).
Decide where you want to go for different days, so when they turn up for morning coffee or afternoon tea, you aren't actually there or are on your way out the door. Because you are on your holidays that you booked because it was so nice and you want to go out and enjoy them. Maybe suggest that you can call over to them later on your way back for the afternoon tea or even the evening meal, and that you will really be looking forward to it after all that fresh air (or whatever).
Arrange to go out for dinner one evening and have a table for 4 booked, or tickets for the local panto, or whatever.
Basically, take back the power.
You are making your own plans and they will just have to fit in with those as they were not invited. This is YOUR family holiday and YOUR family Christmas, and they can be part of it but on your terms for a change.
And yes, they definitely need to be put in charge of various elements (while having what you want done in the background - like your kind of gin or a nice bottle of bubbles or a specific cheese).
In fact, as you will be in accommodation that is not familiar, and won't cater for 6, they will need to bring certain elements with them or they cannot happen (like FIL's favourite veg dish or MILs favourite sauce). And it is up to them to make sure that there is enough crockery for them too - as you booked a place for 4 people and that was all you expected to feed.