Possible meanings are 1) "on us" is a metaphor that means they feel guilty for their transgressions and sins or 2) "on us" is a metaphor that means they realize that Yahweh is punishing them for their transgressions and sins. (See: [[rc://en/ta/man/translate/figs-metaphor]])
"we are rotting away because of them." Being destroyed because of sin is spoken of as if the person's flesh were rotting. AT: "they are destroying us" or "they are killing us" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The people ask this question to emphasize that they have no hope of living. AT: "We have no hope of living." or "We will certainly die." (See: [[rc://en/ta/man/translate/figs-rquestion]])