I hate spoilers as much as the next guy, but even then I know when there's a level as to how far you can go before being absurd from fear. I normally have a rule about games about to come out, I refuse to talk about it or visit their forums the last week before the game launches to prevent any spoilers. However, when StarCraft 2 came out, it was the last day before the week countdown, yet someone decided to post the ending in caps lock as a title in the general forums section.
Now, Blizzard moved quickly to delete this, but as you can tell, the damage was already done. Many people knew the ending now, and I was one of them. And you can trust me when I say that waiting for twelve years for a game just to be spoiled the ending before I can even touch it, I was beyond pissed.
However, I learned that while the ending was lost, and that did suck indeed, there was still many parts of the story that I did not know yet. And regardless if they were to tell me them all, it wouldn't stop my experience from being any less fun.
Your brother is being a bit extreme. Almost every game that is launched lately has some sort of plot twist, or it'll be too bland or too black and white. Tell him, that if he is so afraid of spoilers, then he really needs to learn how to fight his fear, or let it consume him. Because trust me, once he starts to hang out with his friends more often later on, they won't be so hesitant to reveal any spoilers as you are.
My two cents, and good luck on the situation, my friend.
