Right, you and your DH have decided to allow this. That's fine - it's on you.
The trick now is to make it as painless as possible. So, figure out what that looks like for you. A few suggestions:
Let everyone know now that you are definitely not cooking on Boxing Day/whatever day you can't face it. Ask if they want to be in charge or to book something out, as otherwise it will be bread and leftovers and they must help themselves.
Pre-plan some events or activities to relieve the pressure. This could be events/activities WITH the family visiting, or it's also okay for those to be with your friends. eg I imagine that, Mary and Jane always get together for an afternoon of shopping in the salse followed bt dinner and drinks on aroujnd the 27th or 28th?!
Ask now for what help/contributions you would like people to provide. MIL to bring Christmas crackers and mince pies, SIL to plan breakfasts. Everyone to bring wine. etc etc.
Normalise in your own head being comfortable wandering out to do your own thing without having to entertain them - the shopping, getting your nails done, walking the dog, going to the gym etc etc. Be prepared to casually pick up your handbag and go, without having to justify it.
Finally, make sure your DH is 100% stepping up with prep and during their visit activities and chores. Whether that's getting rooms set up, changing bedding, shopping, cleaning etc.