Under the New Covenant, Gentiles can be grafted into the commonwealth of Israel and be partakers of the covenants of promise. (See Ephesians 2:12)
ONLY the people who have faith in Jesus are grafted into the Israel of God --
And ONLY those who are obedient will remain in the kingdom.
Here, Jesus makes a clear distinction between his natural family as He identifies his true BRETHREN:
“And it was told him by certain which said, Thy mother and thy brethren stand without, desiring to see thee.
And he answered and said unto them, My mother and my brethren are these which hear the word of God, AND DO IT." Luke 8:20-21
The heathen and disobedient Christians are NOT Christ’s Brethren!