As a Kiwi, I say you should welcome them with open arms.  I know that there's a relatively small window within which elderly parents are able to travel.  While it might not be your ideal Christmas, it will make fantastic memories for your children and give their grandparents a great deal of joy.  Perhaps you could include your family too, to make it more of an occasion.
Why not buy them a surprise Christmas present of a few days away during the time they are here to Paris, or somewhere like Bath, so that you have a bit of family time, and they get a bit of a rest, as well as seeing another part of the world while they are here.
As others have suggested, you could always find an Airbnb close by - they may be happy to have somewhere to retreat to each evening.
 

I was abroad from my parents and missed out on so much: as did they. To see grandchildren needs to be holidays with busy term time schedules for children.
Other cultures automatically include grandparents with joy.
Discussion needs to be up front and maybe 2 weeks is enough? How open is the 3 sibling discussion on how to do this going forwards?

I dread my kids marrying an Australian or Kiwi and going to live on the other side of the world. I know it’s hard for you as I’m sure you want a Christmas with just your family. But as others have said you have to imagine it’s your child who has moved to the other side of the world and their spouse doesn’t want you going to see them at Christmas. How would you feel about that? That probably gives you your answer.

Try and see it from the point of view of the in-laws : they live on the other side of the world from their grandchildren, they cannot see them grow up or have an ongoing relationship with them. They cannot be there for them after school or watch them play in matches, so they try and make up for it by being there over the holidays. And they will be very conscious there is not much time before they are too old to travel. How would you feel if this where your grandchildren?

Said from someone who moved here from abroad over 20 years ago and now regrets foisting such a separation on the family. At 25 you don’t really realise how huge a sacrifice you are imposing on your loved ones.

Tell them you are redecorating over Christmas and you will see if you can get a short term flat rental for them nearby.Or a cheap hotel rental for the period. If they call your bluff or do say go ahead you can always cancel your decorating at the last min too late for them to come!
Then there is the covid stuff explain you think there might be a lock-down.or any other political reason you can think of.
Maybe others can think of plausible cancel-able reasons!
 

My view is that etiquette applies to everyone, including family. If they want to do a surprise visit, great, but then they need to arrange their own accommodation. Whenever we go anywhere to stay with someone, we give notice. It’s the polite thing to do. Setting boundaries includes telling them that it is wonderful they can come, BUT you have already planned things and will see them often but not all the time etc. I had a similar thing happen with my parents this year, who decided to holiday in the same place as us. I explained to them that we want to spend alone time together as a family, but that we will see them too. I also explained that because of that they can’t stay with us. They understood and were fine with it. In-laws are more difficult and I’d get your husband to manage that relationship. It is his job to do that after all.

My view is that etiquette applies to everyone, including family. If they want to do a surprise visit, great, but then they need to arrange their own accommodation. Whenever we go anywhere to stay with someone, we give notice. It’s the polite thing to do. Setting boundaries includes telling them that it is wonderful they can come, BUT you have already planned things and will see them often but not all the time etc. I had a similar thing happen with my parents this year, who decided to holiday in the same place as us. I explained to them that we want to spend alone time together as a family, but that we will see them too. I also explained that because of that they can’t stay with us. They understood and were fine with it. In-laws are more difficult and I’d get your husband to manage that relationship. It is his job to do that after all.

Like your husband I live far away from my family and really missed them especially at festive seasons. If the in-laws are pleasant people I would suck up and put up with them. At the end of the day my view is they are a lot older so it is “limited” time on how long you need to put up with them. Plus it is not something you can always defer to the future as you never know what might happen. My friend was complaining having to host her parents from Australia for 5 weeks over the summer and couldn’t wait to get the house back for themselves, and her father who was healthy died of a stroke a month after returning to Australia. So life is unpredictable.

Hi, hoping some expat families might be able to help me. I am married to an Aussie and we visit his parents every Easter with the children for nearly 3 weeks. They have 3 children (all live abroad) and 2 of them see my in-laws on alternate Christmas holidays, one has never obliged.

This year isn't our Christmas to have my in-laws but without any notice they have just announced that 'surprise' they are coming to us as their daughter's family won't be able to host this year  ... I know that my husband makes a huge sacrifice in being so far away but I am am really cross that we will now be seeing them for 3 weeks at Christmas when they were only here last Christmas and we have been to Aus in between. To make matters worse we have a skiing holiday booked which they would like to join. Of course I will make everything lovely, they are good people and the children are excited but I realise how excited I was to be having our own relaxed Christmas this year.

I appreciate as I am writing this that I seem a bit ungrateful for my lot but I would like to know what other expat families do. Do you suck it up and its the price for being away from home or being married to someone away from home or do you try and draw some lines in the sand so that you get to have some holiday time with people other than in-laws.