I wonder why Jesus did not place Mary in the care of her other sons? My guess, and it is only a guess, is that the half brothers of Jesus, the other sons of Mary, were not born again believers yet. Later some, maybe all, did become BELIEVERS in Jesus, two of whom, James and Jude, wrote books in the New Testament.
:-)
If there had been other sons, Jesus would have done that. But this proves that Jesus, truly God, and truly human was her only son.