Dh's granny always ruins our holidays. She doesn't stay at our house, bc we all live pretty close, but she will never set a time or day for things and will finally tell us one time or day after much nagging, only to change it at the last minute. I've quit trying to rearrange for her and tell her we will be there on the original time or day.
My advice... although this is just me... leave a spare key out and tell them to go on in. You guys have plans with your family and will be back whenever you can. Take your time. Let your dh clean the house or bedroom and tell them that he done it. If its not up to par, its his fault, not yours. Then volunteer him to run out for some McDonald's, or whatevers open, for Christmas morning and explain that you want to enjoy your LOs on Christmas morning and are not planning to cook. You can enjoy it and if they don't like it, then this'll be the last Christmas you have to deal with this crap lol. Maybe that's a little blunt, but that's what I do. Christmas is for family and my kids. I refuse to cater to anyone else. My kids and these memories come first.
All of this! If they want to stay, fine, too late to say no. That does not mean you need to give up your holiday for them. Take your time, let your DH organise the guestroom and stay the heck out of the kithen! They can get takeaways or cook for everyone, we should enjoy Christmas morning how we choose!