• santanvantaḥ-prajā-tantūn — extending the threads of progeny
  Three consecutive synonym-chunks. Tantu — thread, generation. Kṛṣṇa explicitly licenses gṛhastha-līlā for these kings; bhakti does not require flight.
• sukham-duḥkham-bhava-abhavau — happiness, distress, birth, death
  Four consecutive synonym-chunks forming the standard dvandva of saṁsāra. Listed without horror — these are the weather, not the destination.
• sevantaḥ — accepting / serving / undergoing
  From √sev. A striking word — the kings 'serve' even sukha-duḥkha because they have a higher object of seva now (mat-cittāḥ). Reframes ordinary life as offered to Bhagavān.
• mat-cittāḥ — with minds fixed on Me
  Citta on Kṛṣṇa is the operational definition of bhakti in BG 9.34. The chapter's instruction collapses to these two syllables: mat-cittāḥ.
• vicariṣyatha — you should go about / move around
  Vi + √car. Movement is sanctioned — saṁnyāsa is not commanded. The kings will move through their kingdoms, but with mind already gone home.

A boat crossing the ocean rises and falls with every wave; the boatman's eyes do not leave the polestar. Live, marry, fight, mourn, says Kṛṣṇa — but mat-cittāḥ, with mind on Me. The waves are not the problem; losing the star is.