SB 10.44.40

Kaṁsa's eight younger brothers, led by Kaṅka and Nyagrodhaka, then attacked the Lords in a rage, seeking to avenge their brother's death. KB 10.44.40 Kaṁsa had eight brothers, headed by Kaṅka, all of them younger than he, and when they learned that their elder brother had been killed, they combined together and rushed toward Kṛṣṇa in great anger to kill Him. Kaṁsa and his brothers were all Kṛṣṇa’s maternal uncles, brothers of Kṛṣṇa’s mother, Devakī. When Kṛṣṇa killed Kaṁsa He killed His maternal uncle, which is against the regulations of Vedic injunctions. Although Kṛṣṇa is independent of all Vedic injunctions, He violates the Vedic injunctions only in inevitable cases. Kaṁsa could not be killed by anyone but Kṛṣṇa; therefore Kṛṣṇa was obliged to kill him. But as far as Kaṁsa’s eight brothers were concerned, Balarāma took charge of killing them. Balarāma’s mother, Rohiṇī, although the wife of Vasudeva, was not the sister of Kaṁsa; therefore Balarāma took charge of killing all of Kaṁsa’s eight brothers.