I have flu and I want to cancel Christmas

Tell them all that you're not up to it this year - suggest that if they want the family gathering they can still have it at yours but they must co-ordinate the event including all the cooking and washing up. Give them a deadline by which to let you know. If they all decide on other things you will still have enough time to get what you need for a two-person Christmas lunch if you want one and for once get something ready-made if you want. Show some self-compassion. I hope you recover soon. I

At 11 am Katya said she was leaving this thread and at 2pm you give her more advice
She’s left Goldenage always best to check the posts before you or how else can you give advice

Do not tell them they can come and do the cooking, because by the sound of it they wont , if they were that way inclined they would have been helping on previous years. Tell them you are unwell and don't think you will be well enough to host this year, but that individually they can call in over the few days before or after for a drink and a mince pie. If they say don't worry mum we will sort it if you feel that they will say yes, but you must say me and dad won't be helping , if it all goes pear shaped so be it, ( cheese board and mince pies is lovely) they will never learn if you don't let them.