The Pharisees who didn’t believe in Christ were Jewish — did Christ call them His brothers? Of course not. The Bible is very clear that it is circumcism of the heart, not the flesh, that makes one a Jew and Christ’s brother:
Romans 2:28-29 A man is not a Jew if he is only one outwardly, nor is circumcision merely outward and physical. No, a man is a Jew if he is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a man’s praise is not from men, but from God.
Luke 8:21: He replied, “My mother and brothers are those who hear God’s word and put it into practice.”