Hi Andrea, welcome to our little club. We don't often get easy questions here, but for you the answer is easy. Your daughter comes first.
A diagnosis of prostate cancer is not nice and G9 is not great, but every man in his 80s is going to get something like this. It is almost certainly treatable in his case and statistics say the chance of him dieing from prostate cancer are still quite small. He may find the treatment unpleasant and uncomfortable, but that is just one of the penalties of living to a ripe old age.
I know very little about diabetes. I suspect your daughter can live a long and fulfilling life. She has to come first, you come second and your parents come third.
Don't hesitate to ask anything you want about prostate cancer. We can offer lots of help and advice, and hopefully relieve any anxiety you have about this so you can concentrate on the more important things in life.