To expect parents in mid '70's to host Christmas with very young children?

Wow, I’d quit whilst you are behind Op. Every post you put your sister down some more to try and justify your treatment. You sound wholly unsupportive, and now the comment about siding with a nice ex. I can see why you were accused of that.
If this is you trying to put yourself in a better light, I dread to think how she has been treated. Maybe read your posts and have some self reflection. Maybe her behaviour you are so keen to admonish her for is attributed in some way because of your families black sheep attitude towards her.

Oh dear, condescending much...

I kind of got a bit stuck on your sister is single 'by choice'. What does that mean for goodness sake?
Your sister's children are a year older - your parents are adults and can make their own decisions.
My parents in mid-70s looked after my sister's three children under five years of age for over a week when my sister and hubby went overseas for a wedding - how people can cope is not about age but their individual health and desire to look after kids.

Here’s a tip. If you don’t advocate slapping women, don’t write that women should be slapped as this may cause people to think that you think that women should be slapped.

I'm probably nearer to your parents ages. I would hate one of my children to be alone at Christmas with her children. You say she has a social network but they will probably all also be with family for Christmas. Also, how often do your parents see your sister and their grandchildren? They may well look forward to seeing them. If you and your brother have in laws to see as well, do as we used to do and alternate. One of you -plus family- could visit your parents over Christmas this year and the other next year, alternating with the in laws. That's what many people do.
If you chat with your parents instead of trying to wrap them in cotton wool and not ask their opinion I suspect you will find they want to see your sister, either with or without you or your brother.

I appreciate you trying to put Op in a good light. But her comments about her sister are dripping with judgement, actually make that cascading with judgement. it’s clear she doesn’t like her.
She wants her sister with two small kids who can’t talk to sit by herself for the whole Xmas. Whilst her and her brother have a big family Xmas.
She came on an internet forum to ask strangers how to make that happen.
And you are quoting my post to defend that? Poor!

showmethegin · Today 10:12
So you want your parents to go to you or your brothers and your sister isn't invited to either. So you want your single sister to spend Christmas alone with her young children? Have I got that right?

It’s a difficult situation, the OP is being protective of her elderly parents. The single sister could help and be less obnoxious and then it wouldn’t be so stressful for the grandparents.

Valid information to feed into the 'who's going where at xmas?' shenanigans that start in about August. People without in-laws are usually high value counters!

I’d love the sister to give her side of this story! Maybe she’s on Mumsnet?

I have a 12yr old and in that time neither my parents or my in-laws have ever hosted us on Christmas Day. I can’t remember the last time I even saw any of them on Christmas day. They are all early 70’s, healthy, nothing wrong but all prefer not to spend the day with their adult children or grandchildren. I appreciate it is very weird to others but we the adult children have had to just get on with it and create our own Christmas days at home in our own family units. They never provide any help or childcare either. Not sure why any of them had children tbh but I guess it was just what their generation was expected to do 🙄

I am not sure in today's world 70s is automatically "elderly". I know people in my extended family in their 70s who are very well, fit and active

To clarify it was by choice to avoid anyone feeling any sympathy on that front about her being alone on Christmas Day.

Likewise the highly paid/ professionally successful comment to about any struggling single mum pity.

Agree.

Agree.

OP, your attitude toward your sister is poor.

Also, you come across as oddly possessive of your parents.

Like I said, OP, this person who advocates slapping women who don't please you ("fuckin good" slaps at that), and who also makes ridiculous and baseless extrapolations, is one of your supporters.

Make of that what you will. But don't slap anyone. (I'm sure you wouldn't, but this person seems to find it acceptable.)

I'm trying to understand stand what her unmarried status has to do with the price of fish?

You don't sound dreadful to me OP. I have (I think perhaps most of us do have) issues with a sibling so I can feel your frustration in your post but also your desire to do the right thing by your parents and your sister and wider family. I would say ultimately that your parents should make their own choice. Perhaps you could visit them at some point whilst your sister is there to help support your parents with the demands of hosting. And if you go out for a lunch together, you manage the bill to make sure everyone pays their own whack.

Christmas brings so much bloody stress when it's supposed to be a beautiful time for families and friends and the season of goodwill and all that stuff!
I sincerely hope you come to a happy compromise and you all enjoy a lovely and peaceful Christmas.

The OP has already said she doesn’t live in a big house and her sister’s place is smaller because she lives in a much more expensive area. She’s also said her sister is a sole parent but surely that is a factual description not a moralistic judgement. You’re reading and interpreting more than is there. Her sister won’t compromise, insists 5 days is reasonable and doesn’t help at all with the shopping or taking responsibility for a meal. Surely if part of the reason for visiting is to give grandparents time with the children, the daughter could cook one meal. It is a genuinely difficult situation being fair to the daughter means being unto the parents (grandparents) but given the selfish and difficult behaviour of the daughter/sister I can see where the OP is coming from. The sister will get her way because the parents are kind and caring,

I think it's mainly though that I've been trying to sort out the conundrum of my sister for 25 years.

It's not your job to 'sort out' anything, she's an adult!! What would you be sorting out?

Who told us that?

Has anyone asked the parents? 😉