Is there anyway to get both Thadon's Crown AND Nevershatter from Syl in SI? Please fully explain and thanks in advance.
Easily: do the entire SI main quest line. You assassinate one (and get their item) when taking their throne. The other then turns on Sheogorath, and becomes a Priest of Order- who you have to kill in one of the final stages of the quest line, thus getting their item.