You are not being unreasonable because it sounds like you've had a terrible time for quite a few weeks now.
Younger ones don't really get Christmas anyway.
I'd say that the first time anything 'magical' happened at Christmas with our DS was the Christmas just before he turned three, when we decorated the tree after he had gone to bed and in the morning he was so surprised to see it he just sat in the doorway saying "wow...wow!" for ages.
That's not the say that the whole thing from start to finish was magical. We don't live in Hogwarts, we still had all the usual non-magical crap to contend with as well 
I find that you have to pick your 'magical' moments, and usually the best ones are also the most simple.
In my experience it does get easier.
As they get older they get to understand it more, and their excitement is lovely. I love watching DS get all shy when he sees Father Christmas, and now he's old enough to help with the tree thats lovely as well. And we do little things like go out in the dark to spot Christmas lights and things.
And we always find a nice day (doesn't matter if it's cold as long as it's not raining) to do our 'mince pie picnic' in the local woods, which is basically just a walk with a flask of hot chocolate and a mince pie each in a sandwich box. It gets everyone out in the fresh air, DS runs off some energy and excitement, and it's one of the things he really enjoys about Christmas that isn't all about presents or money being spent.
But I think the trick is not to try and do too much. Don't put too much pressure on yourself to make every single moment of every day magical.
For example, all this Elf on a Shelf stuff seems like too much hard work to me, too much effort and pressure for little result in our house.
But we did happen to accidentally bump into Father Christmas three times while out and about doing general errands (once in Sainsbury's, once in Morrison's, and once in the town centre) all quite by chance but DS was really impressed and confided in me that he thought this was how Father Christmas knows if you are being good.
There's nothing wrong with Elf on a Shelf if it works for you, but it wouldn't work for us. We do other things that do work better for us.
Just make a couple of traditions that do work for you, don't try and do everything that everyone else is doing, and don't drag the kids about when they are ill to please grandparents who don't understand and bitch at you.
I work odd shifts, and DH works away in the week. We have had to prioritise ourselves this year because we've found that other people are constantly making demands on our time and then letting us down.
We've had friend's cancel with an hour's notice this year, leaving our DS disappointed. They are friends who don't work and have no children, yet apparently the whole of December other than one particular day was fully booked up for them.
We agreed to the one day they could fit us in and then they cancelled with an hour to go because they "didn't feel like seeing anyone" We've tried twice to rearrange and both times they've refused, once because he was planning to be recovering from a hangover on the day we suggested, and once because they like to spend that day alone. We will not be trying to arrange anything else with them.
We've had relatives turn up two or three hours later than we'd arranged, one not really at fault as they had been held up by someone else, one who could have come on time but chose not to because it suited her better to come later.
It's too much, when you're trying to fit your own plans in around other people and your shifts at work. I won't be prioritising these people next year when it comes to making arrangements.
I suggest you do the same, put the children first, especially if they are not well, tell your relatives you are having a low-key Christmas, find a couple of traditions that work for you and do those, and don't worry about every single moment being magical.