I am so sorry to hear about your friend! This is a devastating disease. And you are in a difficult position...family but... I have been there, so I understand.
First, you can really help your friend, and her father, by just BEING THERE. To listen, to encourage, and to love. You are the only one who can judge how far you are able to go with questions and suggestions. Some families would welcome them and some might not.
If you are able to have some influence, you would want to be sure that he is being seen at a place that regularly treats LOTS of bladder cancer patients. The state of the art is changing so rapidly in treatment options, that you want to be sure he is being offered the very latest and best. There is a lot of information on this web site about places for excellent treatment.
As you are aware, stage 4 is NOT a good diagnosis. Your loving support will mean a lot to your "family."
My heart goes out to you.
Sara Anne4