Ì don't do Xmas but I do roasts (actually I now do roasts with my carer doing a lot of it).
Is your kitchen warm when nothing is cooking? Mine is cold so I'd put the turkey crown in a slow cooker with a timer to switch on at 6.00 am (unless you are like me and will be awake then)
I don't parboil potatoes for roasties (I often don't peel them either).
If you don't have a steamer get one.
If you are mashing veg then consider making the day before, mashing and keeping in a pyrex dish that can go in the oven, swede mashed with cram and crispy bacon is one of my favorites.
You can buy all veg ready prepped but if dh is doing the chopping it might be a waste of money.
Put cranberry sauce in a serving dish.
OK so your turkey is cooking when you get up and have a coffee.
1.30 hours before you want to eat get husband to prep all veg, peel potatoes for roasting, slice carrots, prep brussels, peel parsnips and cut some for steaming and leave some in chunks to roast (you might want to do the same with carrots) Put all veg to be steamed in the steamer.
1 hour before eating put a baking tray with your animal fat of choice in the top of the oven for the potatoes, after 15 mins add potatoes for roasting and make sure they are covered in fat, each tine you open the oven shake them up or baste with cooking fat.
45 mins before eating put another baking tray in this one has oil and honey in it.
35 mins before eating open the oven and add parsnips (and carrots if roasting) to the oil and honey baste the potatoes.
25 mins before eating put the steamer on, open the oven and baste veg. The veg sill be cooked in 20 but can happily sit in the steamer.
20 mins before eating If the veg is cooked then you can turn the oven down put another tray or serving dish in the top of the oven, move the veg down a rack.
15 mins before eating put the turkey crown on the dish in the oven to crisp the skin. You can add things like pigs in blankets and stuffing if you are having them
Check how much liquid / fat is in the slow cooker and pour of extra, boil the kettle, get flour and a whisk.
Whisk some flour into the fat in the sc, add boiling water and a stock cube - this is your gravy.
Get your serving dishes out, put roast potatoes and veg in one, steamed veg in another, your crown is already on a serving dish - warn people it is hot, ladle the gravy into a jug.
Have a practice run with a chicken and fewer veg sometime between now and Xmas to get a feel for your oven's timing.