Jesus is talking to [teaching] his disciples. [not just the 12]. In context the ‘them’ are the Jews,specifically those who reject his teachings because their foundation is the oral interpretation of Torah. (The Pharisee interpretation of Torah).
Jesus was not saying that those who had rejected Him had no sin. The Scriptures say that “all have sinned” (Romans 3:23) and “there is none righteous, no, not one” (Romans 3:10). This very verse shows that Jesus didn’t cause them to sin but simply removed the cloak they were hiding their sin behind.
If jesus had not “spoken to them” they would not have sin?! - Jesus, through his teaching of Torah, through His revelation of Torah was revealing their ‘sin’ - but this exposed their hypocrisy - hence the reaction.
Earlier in this chapter, in John 15:21, Jesus said they didn’t know the Father. In John 15:23, He said, “He that hateth me hateth my Father also.” The Jews, of whom He was speaking, already had the sin of unbelief in their hearts, but they were covering it over with their pious acts. When Jesus came revealing the sins of the heart, their cover was blown, and their sin appeared in their hatred and rejection of Jesus. Th ‘oral traditions’ of the Pharisees had ways/routines through which if followed would ensure one’ wouldn’t [actually be] sin[ning]
Jesus was saying these things in reference to persecution, and, as He went on to say in John 15:25, this persecution came through no fault of His. The purpose of these statements was to warn His disciples against feeling guilty or condemned when persecution came. The Word strips people of the disguises they have been hiding their sins behind, and persecution is a natural result.
So ‘them’ and ‘they’ does not refer to ‘the world’ - is was specifically ‘aimed’ at the other [Jewish] religious sects that used Torah, particularly the Pharisees. His ministry was to the Jews - not [at this time] the ‘world’.