diddl wrote "Is it just me who has a horror of being alone on Christmas Day ?"
Well, you may not be alone, but I for one can thoroughly recommend it for a stress-free break.
Of course I have enjoyed many family Christmases - early on, as the youngest with 3 elder sisters, and later, just myself at home with our Mum, sometimes with family visiting (though two sisters lived some 200+ miles away so not a frequent thing).
When I moved here (N Wales) 20 years ago, our Mum also moved, but into a separate home (she smoked, I don't) and then some were spent together if she didn't go away to/with one of my sisters (who, with her husband, his parents and his 3 elderly aunts, went off for family get togethers with his brother and family).
I am able to do whatever I want, including avoiding Christmas music on radio, and with no TV, don't miss any 'special' shows that clash!
As for the OP, I'd just say 'be firm and say No Thanks'. I do this regularly, because year after year the youngest of my sisters invites me.
Nothing against her or her family - we're spread out a bit, her towards York, my middle sister around 50 miles from me, and the eldest down in Sussex. We don't get together often, only once in the past 10 years since the death of our mother.
I did go over some 17+ years ago (they wanted a computer set up) but fitting in with 'their' schedule after living alone for a while was far from fun. On the day I was coming back, I had checked the train timetables and was on a pretty early train (my sister was in her dressing gown when she drove me to the station for a 7.15am departure to Manchester - gave me Saturday afternoon and Sunday to relax properly at home... now I have a cat so a good reason for not going).
Some people just don't understand a "no thanks" even if that's the same answer they have had for 15 years! Now they have a place in France to visit, so thankfully they spend whatever spare time they can over there, either driving (if they have items to move) or getting some cheap flights.
Anyway, ramble about my family over... for NotVeryAmused It does seem that relations between you and your SIL and DB are low, and given their achieving a lack of contact during the year, I really don't see why they should
(a) make a big thing of inviting people (and insulting them by requesting funds to pay for it) and
(b) making abusive comments if you don't.
I can understand that your parents would not want to rock the boat too much because of them wanting to see their grandchildren, but I can quite understand that if Christmas is no 'massive' deal for your family, then the SIL just doesn't understand it (and given your other brother visits his in-laws, it does seem low on his priority to see immediate family).
They do say that it's quite a stressful time, so for all the people who put such high importance on getting together, it does seem they ignore the chance of it not being the 'best thing' for everyone, or perhaps they invite others to enforce a crowd to protect themselves from throttling one another if they would otherwise be having rows all the time!
I had been wanting to suggest your DB should be the one to break it to your SIL that her attitude was selfish, but seems he's too much under her influence. Therefore I can only commend the suggested form of words from Stigaloid on Fri 25-Sep-09 16:09 ( and I laughed a lot at Lexilicious 25-Sep-09 12:25, regarding IOU type 'present' ).
I'd love to stick with hullygully's 'fuck off' as a last resort, but think a gentler response if you get any abusive e-mail/text would be less incendiary - on the lines of "No need to be rude. I'm old enough to choose what I do and with whom." (That might even hint at you having company over Christmas, and you can even encourage a rumour with: I'm chatting online with this geek called WebDude, who loves that Chesney Hawkes track "I am the one and only"... {it has a line 'and you're the one and only you' as there's room for someone else in my life, and yours, I assume!})