Jamadagni then ordered his youngest son, Parasurama, to kill his brothers, who had disobeyed this order, and his mother, who had mentally committed adultery

Expressions researched:
"Jamadagni then ordered his youngest son, Paraśurāma, to kill his brothers, who had disobeyed this order, and his mother, who had mentally committed adultery"

Srimad-Bhagavatam

SB Canto 9

Jamadagni then ordered his youngest son, Paraśurāma, to kill his brothers, who had disobeyed this order, and his mother, who had mentally committed adultery. Lord Paraśurāma, knowing the power of his father, who was practiced in meditation and austerity, killed his mother and brothers immediately.

SB 9.16.6, Translation and Purport

Jamadagni then ordered his youngest son, Paraśurāma, to kill his brothers, who had disobeyed this order, and his mother, who had mentally committed adultery. Lord Paraśurāma, knowing the power of his father, who was practiced in meditation and austerity, killed his mother and brothers immediately.

The word prabhāva jñaḥ is significant. Paraśurāma knew the prowess of his father, and therefore he agreed to carry out his father's order. He thought that if he refused to carry out the order he would be cursed, but if he carried it out his father would be pleased, and when his father was pleased, Paraśurāma would ask the benediction of having his mother and brothers brought back to life. Paraśurāma was confident in this regard, and therefore he agreed to kill his mother and brothers.