“people’s sins.” The text is literally, “sins of the sons of men,” but “sons of men” is an idiom for people and can be unclear in English because some people are not familiar with the idiom.
“and whatever defaming words they speak.” The literal is “whatever defaming words they speak defamingly.” Greek noun blasphēmia (#988 βλασφημία) and the verb blasphēmeō (#987 βλασφημέω) are transliterated (not translated) from the Greek into English as “blasphemy.” In English, “blasphemy” is only used in reference to God. However, in Greek, blasphēmeō and blasphēmia (the noun) did not have to refer to God or a god, although they could, but were common words that were used of someone speaking against another. The primary meanings were showing disrespect to a person or deity, and/or harming his, her, or its reputation. [For more on blasphēmeō, see commentary on Matt. 9:3]. The two uses of “defame” in this verse inflected differently is the figure of speech polyptoton. See Bullinger’s Figures of Speech Used in the Bible.