If you have the slightest sniffle or doubt about a cold and a surgery is pending, you just stay away to be on the safe side. At the least you ask the family whether they want to risk it. I'd do this regardless of whether there was a pending surgery, it's just all the more important when there is that kind of thing. 'Just a sniffle' can be very poor timing for the family if they get it.
Having other children doesn't make up for the one who isn't there or not having the whole family together. It's also more people for them to want to catch up with. My SIL has family he can only see at Christmas so they often go to his family for it. It is only one day of the year. I can see them other times. I admit I felt a bit rejected when it sounded like they were going to do that every year but really, that is their call to make and not worth making a fuss about. That feeling did pass quickly. It is their right to decide to spend every year doing their own thing (and that is what they should do, they have grown up). I know what it's like to have ILs who must have Christmas their way and I don't want to be like that either.
Our children are their own people, not an extension of us. Their families are their own unit, not an extension of ours. I think we feel more tied to our children's families than they do to their family of origin. I think that's quite normal. It's okay to be disappointed when things don't happen like we'd like them to, but it's important to keep that in perspective and think about how we felt if relatives tried to force their will on us.
Please tread carefully if you want to preserve the relationship at all. There are many other days of the year. I know you haven't seen them since March but this has been an odd year with extra distance between people who might normally have connected. If you think you can own rather than try to justify the issue with last Christmas, maybe an apology would be a good place to start?
Times article claim that Waspi women are tone deaf and should read the room



