Inherited cancer. A oncologist.

My paternal grandfather died of cancer in kidney/lung/or somewhere in abdomen, no one knows, before touching the 60 year old mark, my father recently 56 had abdominal pain, diagnosed very little colitis, but he is feeling too weak since then, but abdominal pain is good, but weakness is there, and he has lost over 5 kgs in last 5-6 months, but also he changed his diet and was exercising for atleast 45 mins daily in between may and july, but now he has stopped, he also had sleeping issues though, is this something related to cancer, do we have cancer in our genes my father had older siblings as old as 70 no of them has any cancer yet diagnosed, what are the chances he has cancer and what that i will have cancer, which test should we go for before consulting a oncologist.