You sound incredibly closed minded.
What bearing does my husband's career have on me? His career, his problem?
Oh nothing at all, it's only how we finance our home and all the people in it. No biggie.
Why would MIL think I'm "shit" if she didn't receive a birthday card? Because I've known her for over a decade. She is someone I hold dearly. But in your weird chain of thinking, "not your mum, not your problem". Of course she'd be upset if I forgot her birthday, rightly so. She's family. Equally as upset that DH forgot.
Jabs, girl twin was howling (because jabs) and I didn't join the queue there and then to rebook, when I also had poorly boy twin to get back too. They weren't cancelled, he just woke up unwell, and the appointment was about an hour later. No, I couldn't just call ahead (pointless with an hour to go) and cancel one, and rebook, because I was calling DM to come and look after boy twin, whilst getting girl twin ready, and looking after boy twin. Again, with one DC, these things don't occur to you, you continue with this "well you'd just do what I'd do, there's merely extra children, which hardly makes a difference"
DH not being home? Well I can't ask him to hoover, or fill out the church paperwork, while I cook tea and put DTwins to bed because he's not there. If I didn't have to hoover because he could do it, (which has to be done before DT fall asleep) I could start the dinner, but I have to order things around which family members are there and their needs.
Nothing is left to the last minute, although sometimes things change and that can't be helped. It all sounds very hectic/stressful/last minute to you because you are not in a high mental load situation. It's not hectic or complicated to me. It's simply what's required for a family with multiple DC.
It made me chuckle when a PP wrote "And breathe" after a narrative of a typical less than 24 hours in our household. She obviously saw that as exhausting. It's not at all for me, it's the norm. I'm not stumbling through the day. It's just what a huge mental load looks like. Having a huge mental load, and acknowledging it, doesn't mean you aren't coping with it.