I'll give answers where I can:
It is likely that as the PCa is in your Dad's bones that he has advanced PCa which can be treated but can't be cured. I have advanced PCa. Click on my name to see my treatment profile. Regarding his daily life, it is impossible to predict how it may affect him, however, I can give you hope. I was diagnosed 3.5 years ago. Apart from a period of about one month when PCa gave me merry hell with my left shoulder, my quality of life has been as good as it was prior to diagnosis.
Not all men who have PCa in their bones suffer from pain. So far, touch wood, I'm one of those lucky ones. Your Dad may be too. I hope so. Regarding becoming more unwell, logic says this will be the case, however, I can give you hope again. 3.5 years on and I'm feeling good, enjoying my life, and I'm on chemo!
No one can say. Don't dwell on it. What is past is past. Maybe it was missed but there's nowt we can do about it now. The future is what's important.
Good luck.
David