Welcome, Sandie! Yep, Stage IV is scary, but take heart. My wife is Stage IV, was given 9 months, and is now more than 2 1/2 years from diagnosis. She has fought back the beast several times (see below) and is still going strong.
Your kids have a double load -- fear of losing a second parent, and the reality of their own mortality with two parents having lung cancer. Cancer is definitely a family disease, not just genetically, but emotionally. My best to you all. Don