Your OH can ask your GP for a referral for genetic counselling. They will take a full medical history for him and any known history for relatives, and they will also ask about the areas where he and his family lived and worked, what the wage earners did for a living, etc. They will probably also spell out in detail the pros and cons of going ahead with the test and then send him away to think about it.
We have a brain tumour in the family so I was referred for genetic counselling. By the time we had done two appointments, they had completely convinced me that genetic testing was a bad idea. Apart from anything else, there might have been unintended consequences for my children, such as not being able to get a mortgage when they grew up, not being able to get affordable life insurance, and the emotional impact for them if we found out that I had it. Direct impact for me included possibly not being able to move house in the future unless I could buy without a mortgage. They also explained that it was much more likely to be environmental - my wider family almost all lived in the same few streets, drank the same water, cooked similar food in similar ways (most significant, the use of the same chip pan for many years and not necessarily changing the chip fat very often), breathed the same air from the same pits and shipyards.
It is similar for prostate cancer. Only a small percentage are thought to be truly hereditary (5%), most commonly BRCA 2 at less than 1% of all prostate cancers. If a family carries BRCA then it would usually be seen as breast cancers in 30 year olds, metastatic prostate cancer under the age of 50, ovarian cancer, male breast cancer, pancreatic cancer and cases of childhood leukemia. There are other gene faults such as HOX which are more common than BRCA but have no relationship with breast or other cancers apart from prostate.
Vast majority of prostate cancers are thought to be environmental - drinking water with added chemicals, consuming foods that have had hormones added, plastics in our diet (cling film, drinking out of old plastic bottles that have been left in sunlight, that kind of thing), consuming a lot of processed food. And that makes sense in my head, at least; traditionally, a mother would cook for her sons the same food that she cooked for her husband, in the same pans and possibly that would be the same food that her mother-in-law had cooked before her. When I asked our uro about the risk to our son, he said the best thing we could do was change his diet - get him into a prostate friendly way of living while he is still young. He also said that if society could change the way small children eat now, prostate cancer could almost be eradicated in one generation.