I agree with those who take the turkey out early. I take mine out at least 2 hours before.
Remember you need 12 portions of veg, not 12 portions of each veg. As long as there are plenty of pigs in blankets and roasties I find people are less bothered about missing out on a few parsnips.
I have 4 hob burners so have roasties par-boiled early, then use the hot water from this for carrot and turnip mash, get this cooked and then into a buffet warmer that I got from Aldi a few years back (couldn’t do Christmas without it!). That frees up the burners for the steamer and other veg.
Pre-cook the gravy so you only have to heat up.
Roasted carrots and parsnips also get cooked early and put in buffet warmer, lift lid every now and again to ensure condensation doesn’t make them soggy or put a tea towel under the lid.
That leave oven free for 2 trays of roast potatoes, pigs in blankets and stuffing go on bottom of oven so allow extra time.
If you are using gravy granules boil kettle 15 min early then it only needs a quick re-boil when it’s time to make it.
Write out timings and where everything is going in oven and on hob working backwards from serving to putting turkey in.
As someone else said give people twice the amount of time to sit down than you would think, there is a lot of messing and joking around and it can be really frustrating if you are worrying about food going cold.
Lots of small serving dishes is better than big ones that need to be passed from one end of the table to the other.
Give one of the kids the jobs of taking drinks orders for the meal, get another adult to pour them out in advance. Again saves messing once everyone is sat down and saves space as it means bottles don’t need to be on the table during serving.