For the bigger ones we usually rent a venue, it was a hotel the year we had 100+. Think work Christmas party vibe but infinitely more chaos.
This year it's at my childhood home - big old farmhouse owned by grandparents, parents live there too. I grew up there and there was rarely less than 25 people in the house at any given time so it's built for a crowd. Folding tables and chairs are kept in one of the outbuildings, main meal is eaten in the barn from those which gets emptied and decked out (and heated!!) and is very festive. Crockery, cutlery, place settings, table dressing etc is all rented. Most people stay in the barn and drink and socialise and dance after dinner, grandad always sets up a bar and we take it in turns playing mixologist, heated gazebos outside for people wanting a smoke or some quiet. Kids often go back in to watch a Christmas movie or play on the playstation or something. If the weather's nice enough the traditional Post-Dinner walk happens.
Some years it's catered, some years everyone chips in bringing food. The house has two kitchens so it's just possible to cook enough for everyone if you time everything perfectly.
There's three caravans on the land for workers, these get cleaned and used for extra sleeping space (and cooking space in a pinch), most of the kids do a "Christmas sleepover" in the loft above the stables which my dad does up every year like a giant blanket fort. Couple of my aunties and uncles bring camper vans, everyone else squeezes into the house on beds, sofas, camping cots, blow up mattresses, whatever they can find. Dogs all stay in the kennel outbuilding except my sister's very precious sausage dog who sleeps with her!
It's a squeeze, it's chaos, it's expensive, it's absolutely exhausting, and it takes a month to clean up after, so I definitely envy people their quiet family Christmases sometimes!