This is a metaphor. Here "offspring" means "having the characteristic of." Vipers are poisonous snakes that are dangerous and represent evil. AT: "You evil poisonous snakes" or "You are evil, like poisonous snakes (See: [[rc://en/ta/man/translate/figs-metaphor]])
He was not really expecting them to answer. John was rebuking the people because they were asking him to baptize them so that God would not punish them, but they did not want to stop sinning. AT: "You cannot flee from God's wrath like this!" or "You cannot escape from God's wrath just by being baptized!" (See: [[rc://en/ta/man/translate/figs-rquestion]])
The word "wrath" is used here to refer to God's punishment because his wrath precedes it. AT: "from the punishment that God is sending" or "from God's wrath on which he is about to act" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-activepassive]])