Sorry to hear your dad has been thrown into the world of prostate cancer (PC) in an advanced stage...Gleason 9 with bone metastisis. Outstanding of you to help dig into the disease treatments to help him.
The starting place for you is to understand that your dad's case is "advanced," or "high risk." As you begin "drinking from the firehose" of literature out there, you will find that the vast majority of PC cases are NOT advanced. Once PC has spread to the bones, surgery, for example, is no longer a viable option because the cancer is spread beyond the reach of "the knife." So, skip all the literature about surgery, which can be curative for intermediate risk men, and is usually not even necessary for low risk men.
A course of radiation may be in his future, but most likely it would be palliatively used to reduce bone pain, if and when that begins. Similar to surgery, there are other types of radiation therapy that are used curatively for intermediate (and low) risk men...but dad's not in that situation.
Lupron is a common first-line treatment, and there are lots of other treatment options which will likely follow. The first step is for the Lupron to block the hormones which feed the cancer...to slow it down. PC is almost always a slow growing cancer, even for advanced cases. The treatments available to your dad can help slow it down more, likely for many years and hopefully (likely) until he passes on from other causes.
We do have lots of guys here at HW who are also advance cases like your dad. I'm not, so I'll step back at this point and let others share their own personal similar experiences...
Welcome, and sorry that you had to be here...