I am so so sorry for this diagnosis. ((HUGS)).
My dear friend passed away at age 43 of cancer, my father has cancer, my mother in law has terminal cancer, and my teenage son has cancer. Unfortunately, I know more than I would like to about this horrible disease.
I echo all the advice to touch base with an attorney.
Some other tips:
-If you don't already - set up an account with a service like lotsahelpinghands.org or caringbridge.org to coordinate meals and babysitting. This is a great thing for someone like a friend, sibling, grandma, etc. to be in charge of. You will most likely get a flood of offers for help - direct all of them to the coordinator and have him/her set it all up. On chemo weeks, set up some meals to come to the house. In my experience people will send a lot of food. One way that expenses went way down for us is groceries from the lack of eating from chemo, and meals delivered to the house.
-if you get a coordinator for this type of account, people will ask him/her what you need. I found that people are happy to send "stuff" but are weird about sending money. Ask coordinator to try to steer people towards practical things like gift cards for grocery stores, gas stations, places you already go out to eat. NOT more toys the kids probably don't need, etc.
-Once dear friend got established on a chemo schedule, her group of friends took over to allow her husband to work on the days that were not so bad and bank as many paid days off he could. Then when things were really bad towards the end of her life, he had a lot of paid days off. We would drive her to chemo, and another person would take the kids out to the pool, movies, whatever. Playdate were strategically scheduled on the days she would be the worst after chemo (often day 4 after). Friends would take kids somewhere to exhaust them like the pool for the day, then friend would do something low key like movie night with them in evening with a meal that friends had prepared.
-For my son who does not have cancer, we tried to make as much normal as possible for him as we could. It might be tempting to cut expenses like going out to eat, but to suddenly have that taken away from a child that is already losing so much can be hard. Vacations were already severely limited so that expense went way down. Groceries went way down. We chose to limit the things the kids wouldn't know about - basically savings for FI, home improvements, etc.
-Find out what your yearly max out of pocket is for your health insurance. That is what you will be paying every year for the rest of this journey. Chemo is insanely expensive. We found out that going to a higher deductible plan was actually cheaper for us b/c the premiums were lower.
-Get the kids familiar with things when things are going well. Who will watch them overnight if you have to rush your wife to the hospital at 11pm? Set up a lower key sleepover when things are good - then the kids are familiar with the new house. This is especially important if your younger child has not done sleepovers yet. Same thing with someone else picking them up at school - both for the kids and for the person doing the pick up.
-Set up an emergency phone number list with information. Is grandma going to pick up kids from school ever? Give her the name of a parent from the school she can call with questions so when things are going really bad, she doesn't have to bother you. Get her a copy of the school schedule. Does your wife have a friend who may be helping out who may not have your phone number? A cheat sheet with phone numbers, name of school with time it starts/end, etc. can be very helpful.
-Tell people at work. My husband was able to take 6 paid weeks off during my son's bone marrow transplant and they were all donated vacation time.
-I'd recommend joining some sort of support group, I found an online one to the be the best. I learned so, so much from the group and really knew what to expect as things progressed. When things were going really poorly with my son, having 1 other person who had at least some idea of what I was going through was a lifeline. Friends and family are great, but it is not the same. Both my husband and I have done extensive counseling associated with our son's cancer and would recommend the same.