I can understand yours and your dad's fears.
That frightening word "cancer" is a death sentence isn't it? But that is an initial reaction, born of our own fears and ignorance of the disease. It's a new word in your lives and panic is the first reaction.
Prostate cancer can be incurable but even when it's incurable it can be lived with. We have a number of men on here who have been diagnosed as incurable but who live very full lives and they make every day their new normal.
Pretty well all of us, whether we're the man with cancer or his family, have been where you are now so we do know the process you are going through. No question you could ask is a daft question if you don't know the answer. Somebody on here will either know what you mean or be able to point you in the direction
Ray has given you a link about understanding how PC is diagnosed. If you go to Publications you can download some of the other information on treatments and how to cope emotionally etc. Well worth looking at and perhaps something your dad could be reassured by.
You can also speak to the nurses on this site during their working hours and I'm sure they will be happy to advise you.
If dad is worried about finances you might be able to get some emergency help through Macmillan as I think they have a social fund.
Dad is feeling every ache and pain and has convinced himself he hasn't long left. Have these pains just started or did he in fact have the same sort of pain after his rhabdomyolysis. Couldn't it be that the injuries he sustained then now be making themselves felt even more, and probably stress isn't helping.
If your dad is undergoing surgery, his doctors must feel that he stands a good chance of beating the beast. They can't afford to waste resources if there isn't a probability of a good outcome.
Deep breath and calm down. All is not lost. He and your mum are lucky to have you taking this worry on your shoulders.