I'm sorry about the loss of your husband and your in-laws' attitude to you, OP.
I agree that there is something about Christmas of all holidays that seems to amplify loss. And there's nothing like Christmas (and weddings) for sticklers to apparent 'tradition', for which I read locked into expected ways of doing things. Maybe it's the old rebels die hard attitude in me, but the very word 'tradition' makes me want to stick my fingers in my ears and run off in the opposite direction shouting 'la, la, la!'
I agree with the PP that the music is particularly dreadful! Same old dross churned out on repeat year after year after year - a bit like the Christmas baubles we've had since our childhood but nowhere near as appealing. That Paul McCartney number makes me murderous.
We do low-key. Get togethers are with friends in mid-December and again on HY Eve - for no other reason that we enjoy each other's company and like being together. Unlike with relatives we don't happen to get on with, friendships are entirely voluntary. This makes them amongst the best relationships we'll have in life, and we've now fallen into a pattern where December is the month we celebrate that. I cherish it.
I have lots of fairy lights and two very laden trees (I don't care if two are naff). And we do the turkey. But once the demands of presents (for DC) and cooking are off, it's a holiday that makes few demands on us.
However, the months with short days and long nights will never be my most loved time of year. Easter will always be the favourite holiday: it's spring, everything's bursting into life again, the daylight hours are extending, and it carries none of the conventional obligations associated with Christmas.
This too shall pass, OP. I know where you're coming from: I really do.