I am very sorry to hear about your father. As you probably already know, Stage IV means some cancer was found outside the bladder. He is more than likely trying to adjust to this news himself and contemplating whatever treatment his doctor may have recommended. There are folks here going through chemo in similar circumstances. He might just not be ready to talk about it with you... yet.
I wish I had some advice for you other than to just be available for him when he's ready. Hopefully he will soon realize that it can ease his fears and concerns to be able to share them with family, although I'm sure he does not want to worry you. It is a hard thing for a parent to discuss with a child, especially in the beginning.
If he is a person who would visit an online community, please let him know we are here for him, and for you. We have some members here with grown children who perhaps can offer more insight. I'm sure you will hear from them when they find your post.
Best wishes... Catherine
TURBT 1/21/10 at age 55
Dx: T2aN0M0 Primary Bladder Adenocarcinoma
Partial Cystectomy 2/25/10
Vanderbilt Medical Center