How should we not know that we should turn away from this sin, we who see the fault that causes the destruction of the family, oh Janārdana?

The rhetorical question inverts the moral obligation. If they do not see, we do see (prapaśyadbhiḥ, present participle, continuously seeing). With knowledge (jñeyam) comes responsibility (nivartitum, to turn away, to deviate).

The wordplay pāpāt asmān (from us the sin) — asmān is accusative plural “us” and genitive “our.” We are the ones who must turn away, and we are the ones who must be protected from our own sin.

Janārdana appears again — Arjuna seeks someone who impels (ardana) the people (jana) toward right action, which is precisely what Kṛṣṇa will do, though not in the way Arjuna expects.