Barbara I echo the don't panic messages.
Woolly gave loads of useful stuff already.
If you are new in your house, do you have enough things like chairs and a big enough table? Is there space for such furniture?
Perhaps, especially if the summer is coming, it might be useful to think in terms of multi-use furniture. Like wooden folding chairs that can go in the garden when you have visitors, but also work well indoors for expanding dining capacity. And being folding, they can go out of the way when you don't need them.
And for a table, can you get one that either extends for larger groups, or a second table that can fold away when not in use (Ikea do some on trestle legs etc, or you can get catering type tables that fold down to almost nothing) - again, having for garden as well as indoor use could be useful to make them multifunctional.
And then, while it is quiet and calm, do a lot of thinking.
What do you like to cook? Everything from scratch or everything pre-prepared, or something in between? Are you used to cooking for 2, or a crowd? And do you make a traditional roast on occasion?
What is "expected" for Christmas dinner in your family? Are there specific dishes that are really vital, does everyone want turkey, or is it more that once everyone is together that a good meal (regardless of what it is) is the only important element?
Are there any family specialities that you can persuade others to bring? Aunt Eileen's sherry trifle, your Mum's Christmas cake, brother Jimmy's "ultimate" gravy.....or whatever.
And then start to figure out what you would like to serve for the day.
Work backwards - decide a time to sit down, and then figure out what needs to get done by when to make that happen.
Write that plan down on paper. It helps you to refer to, and also to suggest any willing helpers can look at it to see what they can usefully do.
Do a couple of roast dinners for just you and DH over the next few months, to learn how to do things like roast potatoes and to juggle things happening together.
Keep it simple. Don't go for 21 sides and 17 types of dessert, have some kind of potatoes, some veggies (maybe 2/3 types if you ARE confident) and gravy.
Once you have decided what you want to serve, think about what (other than the family specialities) you can ask the others coming to bring. So maybe someone else should bring the cheese course entirely (cheese and crackers), or the wine, or a dessert that only needs to be served (or MINIMAL prepping in your house - like putting it into the oven or just adding some cream), or a starter (again MINIMAL prep in your house, even more for starter and no oven available).
What size is your cooker? Do you have a second oven or not?
Because you will need to think in your timings about what needs oven space, at what time and at what temperature.
A turkey can come out at least an hour and up to 2 hours before serving (put a double layer of foil over the top and cover with a folded towel, to keep the heat in and let it "rest") - so that gives time to cook roast potatoes and possibly roast vegetables as well if you want.
Lots can be cooked on the stove top or microwave, or even just using boiling water.
Frozen petits pois, left in a pyrex bowl to defrost, and then pour boiling water into the bowl for 10 minutes before serving, cooks them perfectly without using the cooker.
Baby spinach leaves in a colander just need a full kettle of boiling water poured through it to wilt them perfectly.
Gravy can be a huge hassle - or very simple.
You can do the various "make ahead" gravies and freeze, to just reheat on the day.
You can use bisto (other brands are available) powder and make up regular gravy but just add a splosh (highly technical quantity! About 2-3 tablespoons or so) of red or white wine for depth and any juices that come off the turkey. I sometimes use the water from cooking carrots as the water for making the gravy for extra flavor without a lot of extra work.
Or you can buy readymade gravy, lots of them are very good nowadays.
If you have to get crockery etc for the new house, try to get enough for having visitors, even if it sits in a cupboard a lot of the time (and that cupboard could be a spare wardrobe, or under the stairs - just somewhere that it will be safe from damage and that you can get it out when you need it). Plain white dishes can be dressed up with coloured napkins/tablecloth, candles, flowers etc to suit lots of different occasions. And the same with glasses - plain but sufficient wine and water glasses is a useful thing to have. And cutlery. None of these need to be terribly expensive - but if you can have them matching that really does make it look nice - or alternating if you get 2 sets of 6 but in different patterns say.
And a few serving dishes - which can be large bowls or plates just as much as "serving dishes!". Jugs for milk (and can be used for gravy, being washed before tea/coffee course - if you have willing helpers).
Plates can be heated by sitting in the basin in hot water, if your oven is fully occupied - and just get someone to dry them off with a clean teatowel to serve onto.
I always prep my veggies and potatoes the day before - they can even be done on 23rd if you have time then and just keep in cold water, change the water on 24th. (Onions and parsnips don't like water so keep those in airtight containers instead).
And in your thinking, think about who would be useful to ask to help in various ways (DM to help in the kitchen, or DDad to "entertain" great aunt Dotty in the sitting room, or younger DB to do the washing up afterward etc). Or not.
Do you prefer to work alone, would others try to take over/interfere, or can they actually be helpful. If the former, declare the kitchen off-limits until the meal. You should not be doing any clearing up after serving.
And would your kitchen/dining work better to serve each plate in the kitchen, make it a buffet for people to work along and then sit down, or put everything in the middle of the table for people to serve themselves already sitting. Or something in between those.
Night before - empty all bins ready for the following day.
Morning - run the dishwasher after breakfast (if you have one) whether it's full or not - you will need it empty later.
While cooking, have a basin of hot sudsy water and wash pots etc (or have a willing helper) as you go to prevent things building up.
And make sure you have time in your timetable to stop for a few minutes here and there, to just enjoy the day and your DBaby's first Christmas, and your first Christmas in your new house.
And if things run late, that's fine, better to be a little late and throw an extra packet of crisps or something on the table for the guests with a drink beforehand than be totally stressed out and on time.
Sorry for the brain-dump, I hope it makes some sense!