Doing my head in...

Surely the 92 year old should have some say in what she does and if she lives alone can't she be in a support bubble. At 92 it may be her last Christmas, with or without the virus.

Would you prefer the 92 year old to be left out? Surely not. For her safety under present conditions explain your warm concern that you would prefer not to mix at Christmas and look forward to meeting all again after the pandemic. No need for anger or drama.

Another in law problem perhaps? Would you leave your own elderly mother to dine alone on Christmas day?

Silverlady79 it's too soon to know what the "rules" will be by then anyway, but in general the fewer people who mix the better.
That being so, it isn't unreasonable for your in-laws to see their mother, but to minimise the risk to all of you it would be best for everyone if the two of you don't go.
With regret, obviously, and much as I'm sure you'd like to... ???

My brother's been making detailed Christmas plans with my Dad involving travel, overnight stay, travel, two weeks plus away, travel back again, etc.... I tried to say it's all against the rules at the moment and not necessarily a good idea anyway, but it fell on deaf ears.

You just need to do what's right for you, as if you're not comfortable with going you won't enjoy the day anyway.

Are they going to sulk if you don’t go?
In the circs you are entitled to decline IMO, and comfort yourself with the thought that Christmas dinner in a restaurant is nearly always ludicrously expensive, and very rarely worth anything like the price.

The way things are going nobody will be seeing each other next Christmas either----literally !

Can I ask where you are, as the mention of tiers presumably means it isn't England?

Regardless, I would say that even if it's legal, if you aren't happy with it, don't do it, though I do realize that's not as easy as it sounds when you have be even brought up to respect other people's wishes!

Being in a bubble doesn’t make you safe from coronavirus. How did this impression become mainstream?

Just say No.

It looks as though the rules might change and allow more people to meet at Christmas, but you still don’t have to go.

It's more important that they see a lonely 92 year old woman than that they see you, if you are young.

I see nothing wrong with this is she and they are in a bubble.

You needn't go to the lunch.

Why do you need to be a "witness" to the lunch? The 92 year old surely will have one with your in-laws... they must be her bubble therefore you don't need to go.

Please don't get cross it's probably easy to cancel. You can always offer Easter if it's safe by then

they might not all be able to celebrate Easter, if they insist on acting recklessly at Christmas.

Easiest not to go, I would think.
No need for drama.

Whoever is in the bubble with their 92 year old mother can see her safely. If you and your husband aren't in her bubble then I don't think it would be safe whatever is allowed at Christmas.
Mixing like this can spread the virus.