You are not being unreasonable, life evolves - just because you knew he worked a lot pre kids doesn’t make it ok that he does now.
It sounds you are both so accepting of him working a million hours a week, you think that’s the way life is, it isn’t.
You don’t know what you want because you are overwhelmed and a feeling of hopelessness that life will never change which is making you feeling helpless. Do not give info this! Act now before you are a shadow of a woman.
Write down all the childcare, admin and chores of family life - all of it.
and then sit down with your husband to solve the problem of divvying it up. You need to do less, he needs to do more, some you probably need to outsource.
Chip away at a system for a year till it’s right. You will not get it right first time. You will need a big white board for the kitchen and an electronic shared family calendar.
Try and divvy up areas completely - he does laundry, you do shopping, he does dentist, you do GP, you do sports kit, he does packed lunches. This way he is forced to take control of his areas - if the kids have no lunches there is only one person to blame.
I’m not suggesting it HAS to be 50/50 - although that assumption should be the starting point - but he has to take on responsibilities, not just ‘help’.
Outsource cleaning if you can (maybe some laundry too), get food delivered, have some ready meals days, and divvy up some batch cooking at weekends (or get someone to do that too).
As for your SIL, you cannot do anything about this immediately, but you can keep pointing it out, and hopefully the family will gradually reduce her hours.
If your husband backs off all this, tell him you think the two of you need marriage guidance counselling - that’ll get him round the kitchen table sharpish. (And if things go on like this, it’s true, you will.)
Also, ask yourself if you have some standards that need dropping. And make some time to look after yourself.