I'm in the 'unreasonable request' camp. Whilst I understand that your in laws may very well be nervous, they shouldn't impose their concerns on you and definitely not your kids who have suffered enough. Unless of course your kids don't mind, you should run it by them.
If they feel nervous about the whole thing - the more practical thing to do would be for them to stay at home, wait for their vaccinations and have a big family gathering in the new year. 
As a parent of two kids, if I said they had to self isolate before Christmas, I would have two very unhappy children. Have a big zoom catch up over a bottle of fizz and meet in the new year.
Good luck whatever you do!

I don't think anyone is being unreasonable here. However the problem is the difference in perception of risk and what sort of isolating your parents in law expect. They may not feel secure unless you do the full test and trace-style isolating, if they've got used to that restrictive way of life, however your teens may think they're being careful if they keep the window open when seeing friends, as they're with them all day at school anyway.

I think it is critical to manage expectations well in advance of Xmas. To stop yourself being the middleman (and potentially the scapegoat), I would recommend that you arrange a family Zoom call, including your teenagers. Say to your in laws that you'd be delighted to have them, but just need the whole family to know exactly what is expected. Then you can have a full discussion about it. Get them to explain precisely what level and length of isolation (can you go to the shops, for example) and whether testing would be a partial solution (do your research first as to when slots are available). Maybe your kids will buy into it - then that's great, you won't need to police them. Or maybe your kids will protest and your in laws will realise it's too big an imposition, so it's better to wait till they can visit more safely.

We did that last weekend. When my in laws realised that my sons would have to miss more school to isolate properly (they wanted 2 weeks), they decided that it was not worth the sacrifice and we will celebrate together next year when they have had the vaccine.
Good luck!

I don’t think there is a compromise by asking your kids to be careful for a few days, viruses don’t respect compromises!

I’ve had to have difficult conversations with both sets of grandparents. I don’t want to bear the risk of them catching Covid over Christmas by spending time with us. Especially when a vaccine is round the corner. I have promised them that that can spend plenty of time with us all in the new year once they’ve been vaccinated.

I think only you can make that decision based on the relationship with your in laws. My own parents are desperate to come down to spend Xmas with my kids having not seen them since August, but understandably really nervous given they live in a really small town and have pretty much self isolated again the last 4 weeks (they dont have room for us to go there).
(Btw, did anyone see how heaving Northcote was on Saturday with drinkers? This was during a supposed lockdown)
The first conversation with my mum seemed pretty aggressive also as she firmly told me we can see friends when they've left and there will be no trips to the pub. After my initial reaction of being told what to do by your mum at 50, I realised it came from nervousness and fright and not because she is trying to tell me how to lead my life. This year is different. I'd much rather not go to the pub, make them feel safe and feel I did all I can to shield them whilst they see the grandkids.

Obviously, these things are very personal and you'll get multiple points of view. I personally think it's completely ridiculous given they are coming to YOU not the other way around. If they are so risk averse, they really shouldn't travel or mix with people at all. If you were visiting them (and actually wanted to), fair enough. So to sum it up, I would politely dis-invite (although I don't know how you dis-invite someone who invited themselves). Also, good luck getting a 15 and 17 year old to agree to a whimsical request given they have been already suffering for almost a year for the sake of older generation.

Of course it is not unreasonable to ask, but I personally consider it a bit outrageous to invite oneself for Christmas and then make demands of the host. But obviously that's just how I read it.

If they're old enough to be particularly concerned by a potential COVID risk, I would seriously thinking about postpone a gathering. Unless your kids are at a private school they'll be in class until one week before Christmas, so I wouldn't be comfortable relying on the result of one negative test. Are they going to be really stressed about everything when they arrive and then not enjoy the gathering anyway?

I don't think this is an unreasonable request, they are simply thinking of their own health, but I also don't think it would be unreasonable to say no and to postpone the meeting until later on next year when it is safe. If I were you, I would discuss this with your children and see if they are prepared to make this sacrifice. It may not seem like a big deal to us, but for teenagers a week seems like a long time, especially after the year they have had. I think it would be unfair to to force this on them, and you do not want them resenting their grandparents. If you can get/afford the private tests for all of you, and you all accept that there is still a small risk, then go for it. If not, I would wait until a safer time.

Not sure if it is reasonable. I don't think you should put this kind of weight on people - i.e. I want to see you but you need to isolate for a whole week otherwise you might be responsible for killing me. I would never ask people I want to see to do it. If I am too concerned about getting the virus I would just plan accordingly. I think I would be agreeing to spend Christmas apart unless it was your choice to isolate

Thanks for all of your replies and for your suggestions.
LFG87 where did you find was a good place for a test? I would be happy to pay for peace of mind and maybe ask my kids to be extremely careful and ask them to stay in for a few days if not a week beforehand as a compromise.

Wow, I can’t believe that you think this is an outrageous request. It is literally for 7 days, how hard is that? I think it is a reasonable request personally but best thing is to talk to your children and husband about it.

I don’t think it is unreasonable for them to ask. In fact it is the reason we haven’t see. My parents in a year (they live abroad and the logistics of isolating after a flight in order to see them are impossible to navigate).

At the same time, you have a 15&17 year old. At that age I would discuss with them; do u Want to see grandparents (and therefore isolating) or you think it would be too tough to isolate. At that age it would be hard to keep them locked in and their opinion and willingness do matter.

I wouldn’t count on a private t at unless you can pre-book it b

Gosh I’m slack-jawed that everyone else seems to think it’s a reasonable request! Of course it’s not reasonable. Unless your in-laws are very close to your kids then if they’re that concerned they should just not come. Teenagers have suffered enough this year and to make them stay in again after a month of lockdown and during the school holidays is just cruel. We are hopefully close to getting a vaccine so your in-laws should stay safely at home until they are vaccinated and then they can come and stay. Please don’t make your kids stay in - they’ll just resent their grandparents and it’ll ruin their Christmas. Offer to get a test (which I think your in-laws should offer to pay for) but don’t agree to this outrageous demand!

It is a completely reasonable ask. Teenagers being cooped up vs parents dying is a no brainer - not sure how it can even be a debatable point? Also given what I’ve seen teenagers doing on the common before during and after lockdown- the irresponsible behaviour probably means they’re higher risk than other kids. The other solution of course is just not to spend Christmas or any other time with them this year until vaccines are rolled out.

We are voluntarily self isolating from the day schools break up so that we can see our parents without potentially killing them.

I don’t think it’s unreasonable to ask, no.
I think a better option would be to pay for testing 3 days before and self isolate while you wait for results. I expect it might be booked up everywhere for tests tho!

We’ve been back and forth on Xmas options with my in-laws and have decided to give it a miss this year. They’re 82 and 89. We’ve all been so careful for 9 months and it seems crazy to put them at risk when we’re so close to getting them vaccinated.

We will all be sitting on the footpath outside their place however for a mulled wine on Xmas eve - do just step around us if you see us in Clapham!!!

I think it is fair enough of your parents in law. Think about whether you would want to be held responsible for any consequences? I don’t like to take the risk this year. We haven’t seen my parents this year apart from once in the summer when I self isolated with my 9 month old and 3 year old then got tested before visiting them too