Dr Ignored Fathers Complaints For Three Years, When He Got A New Doctor He Discovered Colon Cancer And He Died Shortly After

My father had been complaining about an issue for the past few years and that his Dr was dismissive of his complaints and wouldn't order a colonoscopy because my father was "too old" at age 80 when I finally convinced him to switch Dr's they immediately ordered a colonoscopy and unfortunately discovered a very large tumor that had been growing unchecked in his colon, he passed away 8 weeks later on Christmas. My parents are divorced but also shared this Dr and when my mother went in complaining about a sore neck and a lump, this Dr said it was nothing to worry about, she went to get a second opinion and it ended up being Thyroid cancer. It seems to me like this Dr cant be bothered to do anything. Should I pursue him for this?