@pofpof, I'm so sorry to hear of your father's diagnosis. Having the diagnosis is definitely the worst, but being the caregiver of someone with the diagnosis is a close second. I see how much my wife struggles with my ongoing journey.
That being said, there is a key piece of information you've left out: does or did your father smoke? Smokers and nonsmokers tend to get different types of lung cancer with different treatments and different prognoses. A tissue sample is the gold standard in biopsies. Liquid biopsies are a new idea primarily aimed at those people where a standard biopsy is very difficult or not possible. Lung biopsies, an MRI, and biomarker testing are the next steps.
It sounds like you're dad's current oncologist is really on the ball. By all means, direct your medical questions to him or her. A good oncologist knows how hard this diagnosis is on the family members as well as the person involved. Once your father has a diagnosis and a treatment plan, members of this site will be able to share their personal experiences.
The good news is that lung cancer is more survivable than ever. As I say in my presentations, "This is not your parents' lung cancer." I was diagnosed seven years ago, became stage 4 five years ago and am still working full-time at a job I love. True, I'm a mere 65 years young, but I don't remember hearing about anybody that lived this well with lung cancer for this long before now. And my friend is still working as a personal trainer eight years after a stage 4 diagnosis. Hope is the byword of all survivors and caregivers, so stay positive. I wish you and your father the best possible outcome.