@caregiverwife , I'm sorry to hear that you are both facing this uncertainty, and the stress that goes along with any health issue. It sounds like his team is on top of this; rescanning after three months and ordered the PET scan.
When I've faced similar situations, I try to focus on what I know, not the speculation that's swirling in my mind. It helps me from jumping to the worst-case scenario.
Our lungs are sensitive and react to many things. Are you working with a pulmonologist? Have they talked about trying to biopsy the largest nodule? Have his CT's shown any lymph node swelling?