Mine is Stage 4, but it turns out it's secondary to Primary lung.
First symptoms appeared for me in January this year, am still here in September! Had steak for dinner tonight, then talked on phone with friends for about an hour!
I think you need to go with your dad to appointments and find out what the 'treatment plan' is going to be, and read as much as you can on this site so that he has a better understanding of what's proposed.
Give as much info as you can and you'll find lots of useful suggestions here.
Brenda