I'm so very sorry. Spend the money, take the time you have with your family and create some memories. Do the treatments.
A friend of mine in NYC was also diagnosed last year (a month after giving birth) with an inoperable brain tumor. They took out what they could and she's been going through a targeted radiation treatment that is surprisingly working at shrinking the tumor. It hasn't been easy, she had a few close calls after the surgery but her prognosis right now is much better than it was last year at this time.
Some things from the passing of my father. Make sure your wife's name is on all of your accounts, and that she is the designated beneficiary for each. Also, my dad had created a "when I pass" book. In it he had all of the accounts, where they were located, passwords etc. Also had a list of people to call and phone numbers (like SS office), an outlining of his funeral wishes, copies of his birth certificate and SS card, an explanation of how to do the probate and what forms needed to be delivered where, and letters to each of us. In the cloud of grief, that thing was a life saver.