Merry Christmas, belatedly! 
My poor darling SIL did Christmas lunch for 10, plus supper and breakfast, then again for 14 on Boxing Day. She has unlimited funds and a huge kitchen with a conventional oven plus an aga but even so...
Trouble is, she puts it on herself. My DB cooks all the rest of the time. It's only when entertaining that she insists on cooking. And of course she got lots of offers of help, all rejected, rather tersely. She did let me finish the canapés but only that.
This is a very high flying, hugely successfully woman. I guess she sees Christmas catering as some sort of test or goal. It's a shame because although she's very cordial she never really relaxes. My DB tries to help but she won't let him, though he does all the drinks. The adult DC do the veg and their DD iced the cake.
I just wish she would let us do more. She's a love and I wish she didn't push herself so hard.