I think there might be arguments!

FarNorth, the OP actually said that it was the vegan daughter who was likely to have a hissy fit. That's why many replies are responding to this.

I wouldn't eat meat, but I always say how lovely it is to have someone cook for me. There's usually plenty of other things to fill my plate with. Very occasionally I come across someone who thinks a veggie only eats vegetables!

I've cooked meals for part-veggie (i.e. eat fish), veggie, vegan, non-living foods (i.e. vegan & no yeast) and Muslim. I keep spoons & cooking utensils separate. I cook veggie for the Muslim friends because I disagree with halal practices. However, when I go to veggie etc houses I'm served their veggie etc food - and I always say "very nice" - at the Muslim household I'm too polite (scared of appearing racist?) to refuse halal meat. I was brought up to be a good host to guests and as a guest to be good to the host. Maybe when I start to lose my marbles I can be rude & say "not bl**dy lentils again! ?

I notice there are far more negative comments, on here, about the possibility of DD (vegan) causing difficulties, rather than DS (meat eater).
Either seems equally likely, to me.

Quite right, sluttygran to tell them both to behave.

Whose home is this?!!

I would point out that constant nagging and preaching is the last thing that is ever going to convert people to her point of view. If she can be relaxed and cheerful and accept other people's views they will begin to think what a pleasant person she is and might like trying a few of her ideas.

sluttygran I am glad you have a plan!

It sounds like you hit the nail on the head - they enjoy the argy bargy about the subject! As a member of a family of opinionated people, I completely get this. The problem is that outsiders don't realise we're not going to start with the fisticuffs!

This is going off topic, but my Dad stood in for someone at our office quiz once and I only found out the next day that sometimes our team mates daren't say a word when me and my Dad were 'discussing' the answers! That was the first time I realised not all families were so vocal! In fact, when I was having speech therapy I had to learn not to speak before breathing in. I had grown up speaking on my 'residual' breath and this habit developed from childhood through speaking at a point where I could get in my 10p's worth! I told my brothers and they too realised that they spoke on their 'residual' breath and it was a real eye opener. It's a hard habit to break though, so I wish the OP the best of luck!

Good luck sluttygran I am sure they will all appreciate your efforts. I hope you have a lovely family Xmas.

Thank you so much everyone for your very helpful suggestions. I have now decided to prepare dishes to suit everyone, and to tell them that the first person to start an argument will be shown the door!
They are very good children, and always kind to me, but they do enjoy a good set-to over this particular issue. I don’t enjoy it, and it’s my home, so they will have to shape up!
Some very good suggestions for recipes and further reading, also, so my rant has been much more useful than just a chance to let off steam!
You are a lovely lot, so I hope you all have a Cool Yule and a blessed New Year! X

I think all of us face problems with friends and family with eating restrictions of all kinds, whether principled (vegans and vegetarians), allergies or health restrictions.

We have a DGD with allergies to nuts and salmon, both of which foods have been staples in our Christmases. We have decided that the salmon is dispensable, as are a bowl of nuts, I can make my own nut-free puddings, cakes and mincemeat that tastes just the same but when I planned a venison casserole without chestnuts, even DS and DDiL looked horrified. So I made a venison stew, without the chestnuts, then put portion for DGD aside and added mushrooms and added chestnuts to the rest before freezing them.

Much of the Christmas meal vegans and vegetarians can eat: roast potatoes, all the vegetables, stuffing. A Christmas pudding, probably acceptable to all, can be made using veg suet and egg substitute. After that you make accommodation - a nut roast, one portion of vegan 'cheese' and some vegan chocolates.

I would take both children firmly aside before the event and tell the vegan the adaptions you are making and make it clear that her principles are her principles and you will respect them, but she has no right to impose them on other peopel, if she wants to sulk on Christmas day, no one will take any notice of her, then tell her brother that he is not to goad her in any way, in word or deed. Just eat his meat and keep quiet.

PS We had a vegetarian meal that we often have. I didn't cook any bacon that we often have with it. MrBaggs and I think most nice vegetarian meals are even nicer with a bit of bacon ?

Recently when one of Minibaggs's friends was coming for a stay over and would eat at our house, Minibaggs told me that her friend is a vegetarian but "will eat meat if that's what you've prepared". That, to me, is the essence of politeness— not imposing your choices and beliefs on others, especially when you are a guest in their house.

I think too many vegetarians and vegans present an intolerant and rather fanatical food face to the world. They need to understand and to tolerate that other people are as free as they are to think and behave differently and it is not the job of other people to be constantly accommodating their limited choices. Vegetarians and vegans have every right to make choices for themselves. They do not have any right to make choices that inconvenience other people.

DD is vegetarian but would not dream of making a fuss about the food.

I'm afraid I wouldn't allow hissy fits. How about appreciating the time and trouble the food will have taken to prepare and cook, and the fact that you're lucky enough to have family to share it with?

After catering for both tastes I would not allow any conflict about what is being served I would have to tell them to grow up and be civil to each other and other guests and to appreciate the time and effort that has gone into the catering for them.

sluttygran do you think your daughter would accept that her behaviour is simply rude?
A few years ago my strictly vegan nephew was visiting from Australia in the summer and his mother thought it would be a good idea for them to join us on a barbecue Sunday! My nephew brought his own nuts and seeds and refused even to eat the salad and vegan options I'd made, I suspect it was because it had been prepared in the same kitchen as meat. He kept himself aloof during the whole afternoon and could have caused a difficult atmosphere if we hadn't all just ignored his churlishness.

I've found a curry buffet with one meat dish cooked in the slow cooker works well. Lots of tasty vegan dishes in Indian cuisine. Just a suggestion.

Whatever happened to manners?
Both children are quite happy to impose their preferences on you and criticise others who don't share them , thus spoiling the meal for everyone. Plus the fact they are also happy to put you to double the trouble of preparing two separate meals, to accommodate their beliefs. Do they offer to help?
Tell your son and daughter before the meal you have provided food to accommodate everyone, and There Will Be No Criticism.

In our family there are everything from enthusiadtic carnivores to vegans. One vegan has celiac disease and one vegan anaphylaxis, being extremely allergic to eggs, all dairy products and sesame.

Xmas dinner is not as difficult as you might imagine. I serve turkey with sausage stuffing, pigs in blankets and turkey gravy, but everything else is vegan and cooked separately, eg roast potatoes cooked in sunflower oil and loads of other vdg. The vegan centrepiece is a festive raised pie made from gluten free flour and veg shortening pastry filled with mushrooms and chestnuts and topped with cranberries served with vegan gravy.

They are brother and sister . Surely the topic has come up before and a solution was found.

Surely your DD wouldn’t be so bad mannered as to create bad feeling over the food choices of others. My DD is a vegetarian but her partner is not and neither is their child. She wouldn’t dream of imposing her food choices on others, and would get short shrift if she did. I am another who is with Wilma on this one. Let her see the lie of the land before Boxing Day.

I d definitely cook for both as you would expect to, but not have any argument over comments etc
The best Christmas I ever had included two Muslims a Buddhist, a Christian, a vegetarian and me a meat eater everything went on the table so each put on their plate what they found acceptable plus a meaty gravy and a vegy gravy We had a ball but it all depends on acceptance

We serve a complete vegan buffet, so there's no faffing about what might or might not be in something, with one huge glorious ham, kept quite separate.
If your DD wishes to fuss and preach at something like that, then she is doing it to annoy, and needs to be called out on it.
Although it is rather expensive, and honestly, you could sit down and sort out the menus yourself, I have found this book useful: www.goodreads.com/book/show/25622732-vegan-vegetarian-omnivore

Tell her (before the day) to respect your house and that it's your decision about what you will serve food wise to your guests. She must come across meat eaters in lots of other places.

Not all ‘quizzing’ is as civilised as yours though sunseeker