The decision your brother and his medical team will be based on many factors, some clinical, some personal preferences.

You indicate some of the clinical data, age, stage, there are other pieces missing which can help the forum provide feedback based on our journey and personal "research."

Did he have a biopsy, if so, what did the pathology report say?
You say it has spread outside the prostate, that tells us he had imaging, what it doesn't tell us is what type of imaging, what were the results, was the cancer found in the lymph nodes, bones, organs, if so, where?
What is his general state of health, any cardiovascular issues, diabetic...
Any family history of prostate cancer?

One place to start is the NCCN Guidelines, they are the standard of care. I've attached those.
The Prostate Cancer Foundation has an excellent guide too - https://www.pcf.org/guide/prostate-cancer-patient-guide/

His treatment decision should be based on the clinical data, his preferences for treatment, balancing quantity versus quality of life and be informed by doing his "homework." The choices will be many...

Kevin