The word "them" refers to apostles and elders ([Acts 15:6](../15/06.md)), and the word "you" is plural because it refers to the apostles and elders present. (See: [[rc://en/ta/man/jit/figs-you]])
Peter begins to speak to the apostles and elders who met to discuss whether Gentiles had to receive circumcision and keep the law ([Acts 15:5-6](./05.md)).