lots of questions - I will try to answer some of them in an order that makes sense.
Because Dad has mets (spread to other parts of the body like bone) he cannot have an operation to remove the prostate; the operation has significant side effects and he may simply be too unwell to cope, plus removing the prostate would not now slow down the cancer.
Gleason is the score they give to describe how aggressive a cancer is but they can only measure the Gleason by doing a biopsy. Because dad was diagnosed with a very high PSA and advanced disease, it might be that he never had a biopsy - do you know?
Has anyone ever said whether he has mets in his spine? Could it be that they said the tumour is pressing on his spinal nerves rather than his prostate is pressing on the nerves? If so, it sounds like he has something called spinal cord compression, which can stop the legs from working and can also stop the bladder and / or bowel. For some people this is permanent while for others it is temporary and the radiotherapy that they are planning to do may be to try to shrink the tumour that is pressing on the spine.
Is he still on hormones or have they stopped all his other cancer treatment while they deal with this?