If your father-in-laws cancer is in his lungs and liver from an original site in the pancreas, it Stage 4. Surgery will not be possible but chemo may buy him some time.
I can understand your fear about your husband and your son. You need to get in touch with an organization such as Pancan and get information on places that are doing work on early detection in high-risk populations. There may be studies your family can participate in that may help not only you, but future families at high risk. Good luck