disclaimer: These are just my inane ramblings from my own life experiences. Your mileage will vary. :)
Pain. Hospice will see to it that he is not in pain. They will make available to him very large doses of the strongest medications for pain to make sure he is always comfortable. Near the end, this dose of pain medication may be so great he is not awake most of the time. I personally think this is a good thing.
What to do to help him. Knowing one is dying is very scary. I envy dogs and cats who do not understand the concept. Most people do not want to be alone when they know they are dying. When a person knows they are dying and they are alone, their mind starts to think about dark and unpleasant things. These are then fuel for daydreams and nightmares. So be with him as much as you can, 24/7 if possible, and reminisce about pleasant events from the past to fuel his wondering mind. Hug often, several times an hour. Tell him you love him. Tell him how important he has been, and continues to be, in your life. Do things to take his mind off his illness. Play games. Cards. Board games. Watch DVDs together. Comedies are best in my opinion.
Future. I do not think anyone really knows. The cancer could spread somewhere new and cause a new set of symptoms. The brain met that was gamma'ed could grow back or a new brain met could start. He may get some itching or bloating from renal insufficiency. He could get better. He could get worse. No one knows. In my opinion though, not knowing is not a bad thing. I remember seeing a movie once, Kull the Conqueror? In this movie, there was a very depressed character who was miserable all the time. The source of his misery was his knowledge of the future - specifically the exact time and nature of his death. All his life was spent obsessing over that one moment to the exclusion of all the joy that could have filled his life had he been blissfully unaware of the future. Take life one day at a time.
This is just my two cents. Sorry I am so long winded. I am touched by your situation. I hope things go OK. Be as strong as you can be, given the circumstances.
-Amnia