It is really hard to stand up to a domineering, central, family figure, when her own brood have been trained from birth into believing this is normal and the people who protest at being rode roughshod over are the ones behaving oddly.
I put off any direct confrontation for a good few years, because of the high octane fall out and because, to some extent, I understood why my husband chose the path of least resistance (his mum could be mistaken for a steam roller when in "MIL hyper drive")
But for myself at least it was worth meeting every shove with a harder shove back in the end.
It wasn't nice or pretty, and it took a hell of a long, stressful, confrontational, shouty, "I KNEW you shouldn't have married her" time to reap dividends , but eventually she stopped seeing me as somebody she could muck about and got wary of taking me on. (When well, she has bipolar I, so when ill and psychotic there is an inevitable backsliding)
I think, what with a sick kid and on top of that being maneuvered between a rock and a hard place" of comply under duress, or "face the subsequent row just when you need it least", you've probably had all the crap you can take this week. So I wouldn't recommend taking up arms right now.
When this dies down what might be worth a try is telling your DH that while you understand how hard it is to stand up to her, especially after a lifetime of being trained not to, you are no longer prepared to be the collateral damage he creates in order to avoid changing his family's status quo.
And just keep repeating that rather than getting sucked into the details of each event.
Cos they do know, under the bluster, that their mum is "doing a mum" and getting away with it in part thanks to their son's habitual collusion.
No guarantees, because every individual set up is different, what with all the unique personalities that go into the mix, but I found that taking on the issue rather than letting it keep flaring up improved my relationship with my husband no end.
Not least cos I no longer go around seething at him for having chucked me under a bus as it were, being dumped not only with a situation I quite clearly didn't want any part of, but being treated like a stroppy git for even the most minor protest that I was far from happy at having my wishes brushed aside in favour of Battleship MIL. Again.
It took a good while, with many ups and downs, three steps forward, ten steps back. And I did have to step out of my comfort zone and start being combative and clear talking (to the point of being downright rude out of sheer necessity). But we got there in the end.
But it took some serious (and rather uncharacteristic) determination, cos she was so used to getting her own way willy nilly that she wasn't going to back down without some major, consistent opposition. It was a hill I was prepared to die on, cos the alternative would have killed off my marriage in the long run. So I stuck with it, even thought here were times when I couldn't even remember why I thought any rather unlikely gain would be worth all the effort and struggle.
In retrospect, while I can't say I'm grateful for the opportunity (if DH were to drop dead, husband 3.0 would be an orphan on principle), it has been good training ground for knocking the "far too polite in the face of others' rudeness for my own good" out of me, so other people tend not to regard me as a good place to practice similar tactics.
Which I suppose is some compensation ( =
The bigger compensation is that now my husband has far better control over his relationship with his mum, having seen that in fact it isn't "impossible" to stand up to her. He is much happier and a damn sight less stressed as a result of having learned to say no himslef, and follow through by sticking to it, it helps us both to know that we now can gang up and say it together rather than being stuck in a divided and ruled situation.
I'd wait till kidlet gets better and you have had the chance to recharge your batteries though. Takes some real effort and starting out feeling knackered and overwrought means you'll run out steam right when you need it most .
(((((((big fat hug)))))))), cos I know more or less how you feel right at this moment in time. And I know the answer to this is often more of gruelling marathon than a quick sprint and then all done and dusted.