Hi scottishlassie,
OK that is a lot to take in since Saturday. The people on this forum will be able to help you process the information, which at the moment is just going around your head in circles.
The first thing to say is that the words "incurable" and "terminal" sound like the same thing when you have no experience of cancer, but they are quite different.
If he is terminal then the doctors think he has a clear path to death, and it is of the order of three to six months. If he is incurable then it means the cancer will never be cured and he will always need treatment, we have people on this forum who have had incurable cancer for over ten years.
If he went into hospital on a weekend with no knowledge of cancer, then no oncologist (cancer specialist) will have been planning to see him. I do not doubt that as part of his treatment for blood poisoning a blood test will have been done and cancer discovered, but I do doubt that anyone was around in hospital on a weekend to give him all the information he needed in a way which is comprehensible to someone already ill with blood poisoning.
The most important figure to help people on this forum understands what is going on is his PSA, the smaller this number the better, if it were under 4 he would be normal, so clearly it is above 4. If it is more than 4 but under 100 he probably does have quite serious cancer. The fact he has been put on tablets straight away and injections shortly suggests his PSA was in the thousands and cancer is present without doubt. Can you find his PSA number and post it here?
I am now going to be slightly optimistic and assume he has been told he has "incurable" cancer and misinterpreted that as "terminal" cancer. If that is the case, the tablets and injections are for hormone therapy (HT) also known as androgen deprivation therapy (ADT). It can not kill the cancer, but it can make it dormant for many months, usually at least two years and sometimes for over ten years. It is effective for about 95% of men, it has side effects they are quite manageable. I was on ADT for two years it was not a big problem.
I think your dad should be asked to be copied in on all correspondence between the hospital and GP. These letters have a lot of useful information, you can post the details on this forum and members can explain what it really means.
Good luck, keep posting within a week or two you will have this sorted out in your own mind a lot better.