OK: What I am taking from OP's posts is:
DPILs have come every Christmas for the past few at least - flying in for a week
DPILs also visited for 2 weeks in summer, and another week at Oct midterm
DPILs just "announce" their intentions, do not ask if they can visit
(I am assuming from the posts that PIL stay in OP's home)
OP's DPs live somewhat more local
OP has not had Christmas dinner with her own DPs for some years as she has been entertaining DPILs
DPs will not eat Christmas dinner in OPs house if DPILs are there also
OP had understood that THIS year, it was due to be her own DPs year to have dinner at her house
DPILs dictate what must happen at Christmas even though they are in OPs house
OP's own DPartner agreed that it was OP's DP's year, but refused to stand up to his DP's when they announced the fait accompli (sorry about all the DPs)
OK - so DPILs have now booked their flights. Presumably to get cheap deal they have booked non-refundable tkts.
Firstly, tell DPILs that this was not what you had expected, you will be happy to see them over the holidays but that you really want some time to relax this year over the holidays.
So you are asking them politely to find a hotel/guesthouse/cottage locally rather than stay with you. And/Or at least rent a car to get around while that are in the locality.
Whether they stay with you or not, things will be different this Christmas. DCs are getting bigger and you will be allowing them to open presents at a time that suits you, and making various calls etc on your timetable. You will, of course, make sure that DPILs will be able to get to Christmas services, but you may not go with them as you may go to a children's service or not at all or the one local to your own DPs etc.
Could you all go OUT to Christmas dinner - would your DPs go for that in the company of DPILs?
Could you talk to your DPs and get them on board to come to your house in DPILs company this year, but that you will have them alone next year?
Bertrand - I often say "my little family" - meaning DH, DD and I, and not including either DPILs OR my own DPs. We are happy to see lots of both - but there comes a point at which you want to enjoy just being your own family doing your own things.