• jarā-sutaḥ — the son of Jarā (Jarāsandha)
  Patronymic repeated from v.20. The use here, in the planning-speech, keeps the demon precisely positioned — Kṛṣṇa speaks of him not as a king but as the son of the rākṣasī who joined his halves: a creature of conjunction, vulnerable to splitting.
• bandhūn — Our relatives
  Bandhu — kinsman. The Lord's reason for action is family. Compare Gītā 1.32–34, Arjuna's bandhu-language — but in Arjuna's case it produced paralysis, in Kṛṣṇa's it produces strategy. Same word, opposite results, depending on whose vision.
• haniṣyati — he will kill
  Future of √han. The verb Kṛṣṇa Himself used in v.7 (haniṣyāmi — I will kill the army). Now used of Jarāsandha threatening the bandhus. The same verb-class points to the same kind of action; only the agent and the morality differ.
• balī — the strong one
  Bali / balī — strong. Adjective for Jarāsandha. Compare Bali-mahārāja, the great devotee-king (SB 8.15–23) — same word, but opposite trajectory: Bali surrenders to Vāmana, Jarāsandha resists Kṛṣṇa for seventeen sieges. Strength is neutral; only its direction toward the Lord matters.

Kṛṣṇa names the danger plainly: if Jarāsandha arrives while we are facing Kālayavana, he will kill our bandhus or take them to Magadha. The Lord's prime concern is His relatives — bandhu-rakṣaṇa. The strategy that follows (Dvārakā) is shaped around protecting them, not around Himself.