Spur, you can't afford to be paralyzed. It may not be time, yet, but if there is not a miracle of major proportion, and soon, you need to help this family make end of life plans. I had to do this with a dear friend. The initial "do you know where your will is?" was met with a bit of shock, but soon the family was glad that I was "making a list" for them. Grim list, but it had to be done. As above, they can only hear, "Fuck! I've got cancer! Fuck! I've got cancer!". They can't think about future needs when the immediate needs are so overwhelming. If you can, and if it's time, you have to be the end of life planner for them. At least help them make a list of where things are. Where is the will? Where is the life insurance policy and what is the name and phone number of the agent. Who can be contacted right now to help with the kids? Are there funeral plans? Has it been paid for? Ask if there are people she wants to see, and contact them for her. You can't tell them what to say, or how to act, but you can give her the chance to see people she wants to see.
They may freak out and tell you to butt out. If they do, abide by their wishes, but make the simple statement "I am here to help with any of this if you want." It may not be time yet, but all the Stage 4 stuff is not encouraging.
My 2 cents in your most difficult situation.