You are worrying too much.
OK, if your grandfather does have prostate cancer, which will be confirmed by a biopsy, a bone scan is routine. It is done because the cancer cells can get out of the prostate via the lymph nodes and have a wander round the body. The trouble is they like to settle down and choose bones to settle on where they will continue to grow. The bone scan will show if this has already happened.
The biopsy will confirm the presence of cancer in the prostate and will also tell how aggressive the cancer is. If it isn't very aggressive, the wait and see option is what the consultant will go for (it used to be called "watchful waiting"). The reason is that a cancer which is not very aggressive will grow slowly, and given your grandfather's age, he's a lot more likely to be killed by something other than prostate cancer.
So to give you a bit of perspective ... in my case the prostate cancer was moderately aggressive, and had I opted for no treatment at all it would, according to the consultant, have taken around 15 years to kill me.
There are two main treatments for prostate cancer, surgery and radiotherapy. Radiotherapy is available in two forms, external or brachytherapy which involves inserting rice grain size bits of radioactive iodine into the prostate. I opted for the latter but, because of my age, had to have a short course of external radiotherapy as well.
I believe there is now a third form of treatment which involves a form of immunisation (well think of it that way anyway :-) ), BUT it is relatively new - as in it was still experimental 5 or 6 years ago - and is likely to be available only to a limited number of people meeting certain criteria. An no, I have no idea what those criteria are !