Then the son of Pṛthā saw there his fathers, his grandfathers, his teachers, his maternal uncles, his brothers, his sons, his grandsons, and also his friends

The moment of vision triggers the collapse. The enumeration is a crescendo of family relationships: fathers (pitṛ), grandfathers (pitāmahān), teachers (ācāryān), maternal uncles (mātulān), brothers (bhrātṝn), sons (putrān), grandsons (pautrān), friends (sakhīn). Each category represents a bond of duty and affection.

The Sanskrit prose is elliptical: “sons, grandsons, friends” (putrān pautrān sakhīn) are possibly the children/grandchildren of others, allies against whom Arjuna should fight. The intergenerational war consumes all levels.

Atha (then, there) marks the exact moment of breakdown — Arjuna sees those whom before he only knew were present.