Truly I say to you

This indicates that the statement that follows is especially true and important.

the sons of men

"those who have been born of man." This expression is used to emphasize peoples' humanity. AT: "people"

"speak"

"the people were saying"

This is an idiom that means to be possessed by an unclean spirit. AT: "is possessed by an unclean spirit" (See: rc://en/ta/man/translate/figs-idiom)