The word "them" refers to Cornelius and his Gentile guests and household. The word "us" refers to the speaker and his hearers and so is inclusive. (See: [[rc://en/ta/man/translate/figs-exclusive]])
Peter finishes his speech (which he began in [Acts 11:4](../11/04.md)) to the Jews about his vision and about what had happened at the house of Cornelius.
Peter uses this question to emphasize that he was only obeying God. Alternate translation: "Since God gave to them ... I decided that I could not oppose God!" (See: [[rc://en/ta/man/translate/figs-rquestion]])