With a PSA so high they probably didn't need to do a biopsy - and you only get a Gleason score by doing a biopsy. It doesn't make any difference to the treatment.
Did anyone explain that he has mets - that means it has spread to places outside the prostate? If so, did they say whether it has spread to his bones, and really important whether it is in his spine?
Was it the GP that came out? Has anyone phoned the oncologist's secretary or the nurse specialist (if dad was allocated one)?
If it has spread to his spine, it is critical that you all understand the signs and indicators of spinal cord compression (SCC). This is when the tumour presses on the spinal cord - symptoms include tingling in the legs or feet, numbness in the legs and legs not working. If dad has mets in his spine and has these symptoms, you need to know whether a) the GP checked for SCC and b) if not, phone NHS direct or get an ambulance without delay. SCC can lead to paralysis so don't take any risks.
The other question is whether the cancer has spread to his lymph nodes. Did dad get a copy of the letter that the hospital sent to the GP when he was diagnosed? If it is in his lymph nodes, that would explain the swollen legs. Alternatively, as Johsan has said, lymphodema (which is what your dad seems to have) can be caused by heart problems or by the kidneys failing.
Is he still having the hormones?