Brethren — That is, kinsmen. He is our brother — They were easily persuaded to believe what served their own interest.
Related Commentaries of Judges 9:3
Judges 9:3
3 And his mother's brethren spake of him in the ears of all the men of Shechem all these words: and their hearts inclined to followb Abimelech; for they said, He is our brother.