Knight-Paladin Gelvor's armor looks so awesome... and then we get a set from his brother and it has those lame pauldrons. Why? Can he be killed and looted?

No. Gelebor is invulnerable and essential.

His cuirass isn't playable anyway, and cannot be used by the player, and it has no female variant.

And you're really willing to commit snow elf genocide for a cuirass...?