I had a cystectomy in 2004 because of bladder cancer. They always remove the prostate also.
For me it was the right decission. My quality of life is excellent, I would say I am at 95-99%. The key is having it done by someone that is an expert at doing neobladders. If your brother qualifies for a neobladder, it is basically a recosntruction of a bladder from some of your intestines. You learn to control and urinate like before.
As long a the cancer ios within the bladder the prognosis is very good. I do not know the specifics of your brother's case, but if the Doctor believes that is the solution I would proceed but would first get a second opinion. There is treatment that sometimes works without the need to remove the bladder like BCG or mitomycin but sometimes if the type of cancer is agressive or has invaded or is close to invading the muscle wall of the bladder they recomend the removal.
If I can assist you in any way please let me know. If he has the surgery he will be weak for a few months but the result for me was very much well worth it. I thank G_D every day.
Luis