The important bit here is the controlling nature. And the fact that she still thinks she is 'mum' - and can treat you and your brother like naughty children when something happens that she doesn't like.
That needs knocking on the head, firmly and once and for all now that you have families of your own. If it isn't, you'll end up having a poor relationship at best. Her attitude will rub off on the way she is with your kids, and it will poison things. 'Oh silly Mummy, well I did TELL her to bring a coat but I suppose Granny will have to sort it out... again! Goodness sometimes I really don't think Mummy acts very much like a proper Mummy does she? What a good thing you have Granny to think of these things...'
It happens so easily with a slightly controlling grandparent. Happened with my gran. Really, really had an impact.
Her reaction was horrible. Utterly out of order. Now, everyone says mean things they shouldn't sometimes. But the trouble is, you really have to watch it with people like this once you have kids. Their attitude is seen and noted. You already say she'd cause WW3 if you reacted as most people would to being utterly disrespected - by becoming more distant.
She doesn't have a right to a relationship with your kids. It's a privielge that's pretty dependent on her respecting you as a mother and your family.
You might want to think about considering a small WW3 now to avoid a massive one in a year or so's time.
'I want you to know that what has upset me so much about your comment when I told you about our pregnancy. It's the fact that it told me that unless things change, and you start respecting me as an adult then we will end up with you not seeing us and the kids very much. No way would you ever, EVER even consider making such a rude comment to anyone else. But I'm still your child and you'll tell me off as you see fit? No. No way are my kids growing up seeing their mum being talked down to like that. I can guess me even saying that is going to make you kick off which is only going to prove my point even more. I can't wait for September when there will be no more childcare. Right now the way I'm feeling it'll only take one morre comment for there to be more more childcare full stop.'