Rare lung cancer fetal adenocarcinoma mutation

Gloria, @gprior, You want to protect your family from more pain and worry. You have all been through so much recently. I don't think anyone would blame you for waiting a bit to make this type of decision.
Your children have watched the cases of cancer in the family, and they may already have a sense that they may be more prone to some cancers than average. Their doctors should pick up on this too if they report the family history at those appointments.
You would be telling them about results related to your husband. These results don't mean that they will have the gene. Even if they do have the gene, it doesn't guarantee that they will get cancer in the future. We're still learning so much about how these genes impact our bodies.
I have a CHEK2 gene that experts aren't really sure what it can impact, but I've had two cancers, so far. I'm living a good life because the cancers were identified and treated. I've told my sister (cancer free) about the CHEK2. She hasn't been tested, but she is aware. You mentioned that your husband's sister was treated for early stage colon cancer and is doing ok. Knowing that they may have a propensity to cancer might help to get diagnosed earlier rather than later.
You could always pass along the information and let them decide if they want to move forward with the gene testing or not. They are adults, possibly taking the burden off of yourself and let them decide may be best. You know your family best. Also know that there are genetic counselors that are very good at guiding people through this process. Sending hugs and wishing you peace.