I'm trying to find a 4 book young adult fantasy series. I read it in the mid-80's and I found it in the juvenile/young adults section of my local library. In the first book, something terrible happens in a temple, and a young prince is sent on a quest to retrieve 4 sacred orbs or jewels. If he fails, some doom befalls the world or his kingdom; I can't remember exactly. The orbs/jewels are guarded by some sort of guardians. I think the series title had Guardian in the title, but I haven't been able to find a series with that title.
In the second book, one of his companions is offered the chance to look through a window that opens beyond the edge of the world. The companion is too afraid and decides not to look.
In the third book, the prince and his companions go to a kingdom of ghosts or of the dead. The nobles in this kingdom had cut off parts of or all of their fingers to indicate their status, the less fingers you had the higher your noble rank was. The prince defeats a villain in the 3rd book by holding up a glowing jewel, which damages his hand, making him unable to play a musical instrument (a harp or guitar, I think).
I think in the 4th book, the prince dies in the end, but the book ends with him in the afterlife with his gods and is checking on his former companions.