In the old house, when the kids were little, my record was 26 - it was usually around 22. We brought tables in from the garden, expanded into the conservatory, used the garden folding chairs for the teenagers (who were less likely to have problems reaching the table 😆). MIL brought the turkey, SIL brought deserts, I did the ham, veggies, vegetarian/ vegan options (every year a different one of the kids was vegan , one whole family unit was veggie).
timings were crucial, due to oven space, so I knew what had to be done the day before. Younger Dsis would come to stay for a week and she and I would open a bottle of red, let my kids look after her Ds, and crack on with military precision. We worked to a list and strict timetable. ExH did the shopping for drinks/ nibbles - he and BIL were in charge of furniture movements- the kids did the table. Loved those Christmases, happy times. My meals were always on time too!
These days the adult DC alternate between me and ExH, Dsis and lovely BIL both dead. Other in-laws divorced / in new relationships ….all the cousins marrried and doing their own alternating with in-laws routines. It’s ExH’s year this year so I will be having a quiet Christmas meal with a friend who is also on her own - and we are both honestly looking forward to it. Very happy memories of the huge Christmases but things change….