With you helping your dad monitor his psa, I'm sure he will be fine. If I was 74 and had a psa under 10, I probably would just watch it. There is a guy in my man to man support group who is 82 and he has a psa of 14, and he said he isn't doing anything until the quality of life starts to be affected.
I'm willing to bet that all disease has a significant heredity factor and people who say that they don't have a family history probably just don't know. Environmental factors ( diet, stress. chemicals, etc.) cause genetic changes ultimately leading to disease.
Your knowledgable and supportive posts on this site are valuable and much appreciated. Keep up the GREAT work!