From the 'working around cancer thing' I can recommend finding local groups for that specific cancer, like even on facebook, where patient share information.
That way you can find out a lot, from struggles with the cancer type/model itself, issues with the system (approval or not of some stuff needed, how to do it and so on), and even doc recommendations. But I must say that I wouldn't expect jerks in that field....
I moved countries (HR to DE) during my treatment, and FB served the purpose of finding out the terms and figuring out the system, in both countries.
Some folks want the community support as well, I was there for the information mostly, and to read about experiences, recoveries, tips and tricks.
I believe in gathering knowledge to build some illusion of having control of that insane situation, so I've read a bunch of text from USA to see how/what can be done, what's expected and so on (since HR materials are insanely limited).
In my case it was thyroid cancer.
My mum had breast cancer, but she is of the type 'don't ask don't tell', to the point that even 10 years later I'm not sure what she really went through or how she coped. She was in some support group but left since folks there would focus too much on cancer and too little on the life itself...
So, it depends what each needs. Your needs and your wife's needs will be significantly different than your MIL's.
I think most important thing is that you keep the communication channels between you open, even if that is 'ok, no talks for now'. And ask each other 'what do you need from me to do for you'.
I can't advise about CH system more than - read reviews and inform yourself as much as possible.
Also, don't be reluctant to seek therapy/counsel for each and every one of you.
We as humans, even though we know we won't live forever aren't born to cope with serious diseases and operations and procedures, with good help is easier. And our friends and family probably aren't either fitted properly to provide such help/support.
I did mine without such help when it happened, and I drowned myself in finding peace in information, I did talk with my mum, and my SO, but for him it was too much (he already heavily struggled with depression and anxiety at the time), and a few friends but that wasn't deep nor healing.
Then we moved country (ok, after OP and final results that it isn't of the 'immediately fatal type' as was presumed before the OP, and that month between initial diagnose and final one was really hard and surreal - should I prepare for my funeral or for the trip to Bali? I was around 35 at the time) and I couldn't speak German and all things slowly crushed me (3 weeks to relocate, and finding a spot in Berlin and bunch of other shit that happened before and after, let's just say that 2016/17 was crazy)... So I ended in therapy sometime later for quite some time and did the grieving and acceptance then. But I was lucky, since 'my type' was 'some easy one' if you can say that for any cancer, but I could afford to postpone self-care until I emotionally crashed. Now it's all good.
What I'd recommend my younger self would be - do not do it alone, seek (good) counselling ASAP.
I wish you all go through this with least amount of stress as possible.
It won't be easy at all. But by staying united in it you can make it through it, one way or another.
About insurance, I'd call them and ask. Maybe they can offer some counsel about it as well, you never know.